How to resize a UIModalPresentationFormSheet?

I am trying to display a modal view controller as a UIPresentationFormSheet. The view appears, but I can't seem to resize it. My XIB has the proper height & width, but it seems to get overridden when I call it like this:

composeTweetController = [[ComposeTweet alloc] initWithNibName:@"ComposeTweet" bundle:nil];
composeTweetController.modalPresentationStyle = UIModalPresentationFormSheet;
[self presentModalViewController:composeTweetController animated:TRUE];

Any thoughts? I am using the iPhone SDK 3.2 beta 4

You are able to adjust the frame of a modal view after presenting it:

Tested in iOS 5.1 - 7.1

MyModalViewController *targetController = [[[MyModalViewController alloc] init] autorelease];
targetController.modalPresentationStyle = UIModalPresentationFormSheet;
targetController.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;  //transition shouldn't matter
[self presentViewController:targetController animated:YES completion:nil];

if(floor(NSFoundationVersionNumber) <= NSFoundationVersionNumber_iOS_6_1){
     targetController.view.superview.frame = CGRectInset(targetController.view.superview.frame, 100, 50);
}else{
     targetController.view.frame = CGRectInset(targetController.view.frame, 100, 50);
     targetController.view.superview.backgroundColor = [UIColor clearColor];
}

Here's a method that works on iOS7 as well as iOS5 and iOS6: (arc)

-(void)presentController:(UIViewController*)controller fromRootController:(UIViewController*)rootController withSize:(CGSize)size
{
    UINavigationController* nav = [[UINavigationController alloc] initWithRootViewController:controller];
    nav.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
    nav.modalPresentationStyle = UIModalPresentationFormSheet;
    [rootController presentModalViewController:nav animated:YES];
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)
    {
        nav.view.superview.backgroundColor = [UIColor clearColor];
        nav.view.bounds = CGRectMake(0, 0, size.width, size.height);
    }
    else
    {
        nav.view.superview.bounds = CGRectMake(0, 0, size.width, size.height);
    }
}

composeTweetController = [[ComposeTweet alloc] initWithNibName:@"ComposeTweet" bundle:nil];
composeTweetController.modalPresentationStyle = UIModalPresentationFormSheet;
[self presentModalViewController:composeTweetController animated:TRUE];
//if you want to change its size but the view will remain centerd on the screen in both portrait and landscape then:
composeTweetViewController.view.superview.bounds = CGRectMake(0, 0, 320, 480);
//or if you want to change it's position also, then:
composeTweetViewController.view.superview.frame = CGRectMake(0, 0, 320, 480);

As of iOS7 you can simply do

composeTweetController.preferredContentSize = CGSizeMake(380.0, 550.0);