Mojo,
We are talking about the difference between abduction/adduction and flexion/extension. This might not be really easy to explain but I'll try. I'll have you try to do the movements so that you can see them easier.
Imagine standing straight up with your arms by your side. When you raise your arms out to your side so that your arms are parallel with the floor, that would be ABDUCTION of 90 degrees.
Moving your hands back down to your side is ADDUCTION.
Now, raise your arms straight out in front of you. This is FLEXION of 90 degrees.
When you put your arms back down but keep going back so that your elbows are behind your body, that is EXTENSION.
Now we will try to combine the two. ABDUCT your arms out to 90 degrees. Now push your arms forward(FLEXION). When you pull your arms backwards, keeping them out from your body, this is extension. (The extension is what you guys are talking about with the elbows going behind your back.) This is similar to the motion of your shoulder with bench press. I'm just saying that you should only ABDUCT your arms maybe 60 -75 degrees as you are benching. Many people may start with their arms ABDUCTED only 65 degrees but when the weight gets heavy, their elbows flare out, which is the abduction and internal rotation that I don't like.
I know I've probably confused as many people as I've just helped but these are all just technical terms used to described human movements. Some other movements you might have heard are pronation, supination, retraction, and protraction.
I know Jon dislikes bench more than I do for various reasons. I don't really like it that much for performance reasons but I feel like you must have balance from all sides of the joint. If it were a performance reason, I like ground based exercises and bench press is usually done on your back. I prefer to do it while on a stability ball using dumbells.
I hope I've helped more than confused. Feel free to contact me if you have questions or disagree.
Mike Griffin
No Excuses Baseball
www.noexcusesbaseball.com