I don't see how the pros of checking over the shoulder at R2 outweigh the cons, especially in two man. You're not going to go to towards the 45 foot line until the pitch hits the mitt anyways, so it really does you no extra good to know that R2 is stealing (unless you are caught sleeping, which is a different story that shouldn't happen).
If you peak, you find out he's going, then stand in the same spot until the ball reaches the mitt.
If you don't peak, you don't know he's going, but find out when you hear defense yelling, see F5 moving over out of the corner of your eye, hear footsteps behind you, and even if you don't know after all that, the catcher standing up to throw should be a hint (if you've waited this long, yes, you have lost a step or two).
But, if you peak, you are compromising a check swing appeal, a foul ball off the foot, a balk (granted, not if done correctly), maybe even picking up a ball in play late because of eye movement as your head swivels back.
Nope. You move with the runner to get the angle as the pitch is being delivered. (Keep your head to the ball just in case.)
This all being said, if I was told to look at R2 at school, I wouldn't say boo about it. But if I was writing the Bible of Umpiring, I would say don't do it.