Are you taking off on a clean section or on the shoulder of the white water? If the tail is caught in the white water, the board will slow down as you pop up and not accelerate forward like on a clean face and so your foot ends up too far forward. So try to get in earlier as it tends to correct the problem.
If, however, you're popping onto a clean face on a steep drop and your foot is still missing the tail pad, then the chances are you're popping forwards rather than up.
Quick solution...
Try the chicken wing pop-up technique (google it). Kink your back leg and put your foot on the tailpad first as you pop up. Not the most elegant solution, but it does get your foot onto the tailpad straight away.
Long-term solution...
Arms further back, below your rib cage, and as you pop up, you should be shunting your board forward down the face. Stay low - don't stand up straight. Have your weight on your front foot (which takes some commitment on a real wave!), which gives you a little room for manoeuvre with your back foot.
Also, if you can go along the face (rather than down and bottom turn), you can get away with your foot being in front of the fins for the first section of the ride and then correct.
Cheating solution...
Get a shorter board!
This works. I really struggle with my back foot being far too forward on anything over about 6'4, but on a 5'10 it's no drama at all
