Many lifters learn the bench press from powerlifters. And powerlifters certainly know a lot about it. But remember, their goal is to lift the most weight possible for one rep, and they often use special lifting shirts.
If your goal is to build size as well as strength, and you lift raw (without a stretchy lifting shirt), then your pressing form will be different. Here's a quick video lesson.
They're one of the most difficult muscle groups to develop, but the cure to your underdeveloped hamstrings might lie in the answer to this question: "Which way do you point your toes during a leg curl?"