Backroll is a trick that people complicate unnecessarily. If you are breaking at the waist, you are leaving too early and probably trying to huck it.
The best advice I can give you is this: Think of your cut like a half crescent. You should continue accelerating all the way through the wake. However, your cut doesn't stop there...you want to continue to cut away from the boat as you are riding up the wake, with your head over your left shoulder (if you're regular). Lots of people say to tuck your head to your back shoulder: don't do this. It causes you to leave the wake way early, and put way too much pressure on your back foot.
Instead, keep your weight over both feet equal, and just look over your left shoulder (basically, look back at the wake wash). This way, when you pop, you will already have your head in the right position to spot the landing.