Multiple "apple-touch-startup-image" resolutions for iOS web app (esp. for iPad)?

I've written an HTML5-based iOS web application and all seems to be working well, but I'm trying to polish it up with multiple startup screens. The iPhone/iPod touch works well w/a PNG of 320x460, as follows:

<link rel="apple-touch-startup-image" href="img/startup_screen-320x460.png" />

I found plenty of documentation that says the startup images for the iPad should, like the iPhone/iPod touch, have the 20px shaved from the height to accommodate for the status bar giving resolutions of 768x1004 (portrait) or 1024x748 (landscape). However, in my testing (currently w/an iPad running iOS 3.2.2), only the 768x1004 (portrait) resolution works (but is incorrect—20px too narrow—when in landscape mode).

I've tried the following (a wild guess based on the functionality of the apple-touch-icon links), to no avail:

<link rel="apple-touch-startup-image" href="img/startup_screen-320x460.png" />
<link rel="apple-touch-startup-image" sizes="1024x748" href="img/startup_screen-1024x748.png" />
<link rel="apple-touch-startup-image" sizes="768x1004" href="img/startup_screen-768x1004.png" />

Only the 768x1004 resolution image works if it's the last link element listed. If the 1024x748 resolution image is last, a gray background is rendered in its stead (but never the 768x1004). So, obviously the apple-touch-startup-image link doesn't support the sizes attribute.

Is this supported in newer versions of the iOS? Is there any way to support multiple startup images? Should I create a 1024x768 startup image? If so, will is be scaled down for the iPhone/iPod touch? Or, should I just give up and not have a startup image for the iPad?

definitive solution for startup-image and touch-icons for iPad and iPhone (landscape || portrait) and (retina || not):

        <!-- iPhone ICON -->
        <link href="apple-touch-icon-57x57.png" sizes="57x57" rel="apple-touch-icon">
        <!-- iPad ICON-->
        <link href="apple-touch-icon-72x72.png" sizes="72x72" rel="apple-touch-icon">
        <!-- iPhone (Retina) ICON-->
        <link href="apple-touch-icon-114x114.png" sizes="114x114" rel="apple-touch-icon">
        <!-- iPad (Retina) ICON-->
        <link href="apple-touch-icon-144x144.png" sizes="144x144" rel="apple-touch-icon">

        <!-- iPhone SPLASHSCREEN-->
        <link href="apple-touch-startup-image-320x460.png" media="(device-width: 320px)" rel="apple-touch-startup-image">
        <!-- iPhone (Retina) SPLASHSCREEN-->
        <link href="apple-touch-startup-image-640x920.png" media="(device-width: 320px) and (-webkit-device-pixel-ratio: 2)" rel="apple-touch-startup-image">
        <!-- iPad (portrait) SPLASHSCREEN-->
        <link href="apple-touch-startup-image-768x1004.png" media="(device-width: 768px) and (orientation: portrait)" rel="apple-touch-startup-image">
        <!-- iPad (landscape) SPLASHSCREEN-->
        <link href="apple-touch-startup-image-748x1024.png" media="(device-width: 768px) and (orientation: landscape)" rel="apple-touch-startup-image">
        <!-- iPad (Retina, portrait) SPLASHSCREEN-->
        <link href="apple-touch-startup-image-1536x2008.png" media="(device-width: 1536px) and (orientation: portrait) and (-webkit-device-pixel-ratio: 2)" rel="apple-touch-startup-image">
        <!-- iPad (Retina, landscape) SPLASHSCREEN-->
        <link href="apple-touch-startup-image-2048x1496.png" media="(device-width: 1536px)  and (orientation: landscape) and (-webkit-device-pixel-ratio: 2)" rel="apple-touch-startup-image">
        <!-- iPhone 6/7/8 -->
        <link href="/images/favicon/750x1334.png" media="(device-width: 375px) and (-webkit-device-pixel-ratio: 2)" rel="apple-touch-startup-image" />
        <!-- iPhone 6 Plus/7 Plus/8 Plus -->
        <link href="/images/favicon/1242x2208.png" media="(device-width: 414px) and (-webkit-device-pixel-ratio: 3)" rel="apple-touch-startup-image" />

I actually got it to work on landscape mode. I got the info here: https://gist.github.com/472519.

The issue is the landscape image has to be 748x1024 (A landscape image sideways, I rotated clockwise) instead of 1024x748.

I also had to launch the app in portrait mode first and then landscape.

I just wanted to offer a combination of answers that actually worked. We found with the answer that was selected, the retina versions of the splash images were not being used. Pavel's answer fixed the retina version for the iPad. The following has been tested on iPhone (Retina and non-retina) and iPad (retina and non-retina).

<!-- For third-generation iPad with high-resolution Retina display: -->
<link rel="apple-touch-icon-precomposed" sizes="144x144" href="apple-touch-icon-144x144-precomposed.png">
<!-- For iPhone with high-resolution Retina display: -->
<link rel="apple-touch-icon-precomposed" sizes="114x114" href="apple-touch-icon-114x114-precomposed.png">
<!-- For first- and second-generation iPad: -->
<link rel="apple-touch-icon-precomposed" sizes="72x72" href="apple-touch-icon-72x72-precomposed.png">
<!-- For non-Retina iPhone, iPod Touch, and Android 2.1+ devices: -->
<link rel="apple-touch-icon-precomposed" href="apple-touch-icon-precomposed.png">

<!-- iPhone SPLASHSCREEN-->
<link href="apple-touch-startup-image-320x460.png" media="(device-width: 320px)" rel="apple-touch-startup-image">
<!-- iPhone (Retina) SPLASHSCREEN-->
<link href="apple-touch-startup-image-640x920.png" media="(device-width: 320px) and (device-height: 460px) and (-webkit-device-pixel-ratio: 2)" rel="apple-touch-startup-image">
<!-- iPhone 5 (Retina) SPLASHSCREEN-->
<link href="apple-touch-startup-image-640x1096.png" media="(device-width: 320px) and (device-height: 568px) and (-webkit-device-pixel-ratio: 2)" rel="apple-touch-startup-image">
<!-- iPad (non-Retina) (Portrait) -->
<link href="apple-touch-startup-image-768x1004.png" media="screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:portrait)" rel="apple-touch-startup-image" />
<!-- iPad (non-Retina) (Landscape) -->
<link href="apple-touch-startup-image-1024x748.png" media="screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:landscape)" rel="apple-touch-startup-image" />
<!-- iPad (Retina) (Portrait) -->
<link href="apple-touch-startup-image-1536x2008.png" media="screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:portrait) and (-webkit-min-device-pixel-ratio: 2)" rel="apple-touch-startup-image" />
<!-- iPad (Retina) (Landscape) -->
<link href="apple-touch-startup-image-2048x1496.png" media="screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:landscape) and (-webkit-min-device-pixel-ratio: 2)" rel="apple-touch-startup-image" />

I can't take credit for any of this, but this configuration works. Just copy and paste, make sure to make the images exactly the size dictated in their names.