How to Headbutt(W) + Autoattack Combo on Alistar

Since Alistar got buffed in the last patches, I want to master him a little bit more. I watched some Youtube videos where people always do the Headbutt(W) + Autoattack while the target is still flying and they say it is really important to get that combo down, especally on Top and Mid.

I get the W + Q combo in 90% but I'm having trouble with W+AA. The W + Q combo does good damage but as soon you have the Sheen you are more mana efficient with W + AA.

I could not find any good tutorial videos for this combo. So here are my questions:

1. When do I have to click for the autoattack? (Alistars animation or target animation)
2. Do different enemies have different flying velocities? (I doubt it but who knows? A Malphite looks heavier than an Annie!)
3. Is ping (~30) or FPS (~60) an issue?
4. What are good ways to practice it? (Besides Bot-games)

Solution 1:

According to the patch 4.15 (the last one atm) :

W - Headbutt
SUCKER PUNCH : Alistar can no longer land an additional basic attack on his Headbutted target as they fly away

So this is not an option anymore, and you can try to master it as much as you want, it is not supposed to work anymore.