Boomer starts with both heels close to the bag but usually just his left foot actually touching the bag (he is LH) and then he stretches to the ball.
A good stretch is often the difference between an out and the runner being safe. You can see that the stretch in this clip is at least equal to one full stride of the runner.
One other thing that I trained him to do is to "present" the ball to the umpire as he does here (assuming there are no other runners on base). I don't know if it makes a difference or not but he seems to get most of the bang/bang plays called his way. Does anyone have an opinion on that?