I use a heavy green band and wrap the part that goes around my neck with a towel. I attach it using a carabiner to the lowest hole on my squat rack and then back up at a 45 degree angle to reach the tension I want. Then I do them explosively focusing on contracting the glutes and hammies and pushing the hips all the way through at the top. I kind of think it is like triple extension at the top. I can tell you that I am leaning back at the top and never go below 45 at the bottom.
Hope that helps.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin