Correct Placement of the Arms or Elbows?

Hello Blender Peeps!

This is probably a pretty unintelligent question to ask especially since I have been working out for a while. Although we always learn things everyday right?

My question is in terms of a Chest Press and Chest Fly (the exercises when you're laying on your back). I've seen different trainers and people places their arms and elbows in different spots and I always wonder what the exact proper way is.

For example, when I'm watching people do Chest Presses I mean before you go into the press when your upper arms are on the ground or slightly above the ground (I hope that makes sense), I've seen some people's elbows above their shoulders, some people's elbow in line with their shoulders and some people's elbows below their shoulders. The same thing with Chest Flys too. Their arms go above, in line or below their shoulders.

For me personally I always either have them in line or slightly below because I feel like above the shoulders isn't proper form. What makes it even more confusing is when different trainers say different things then you get all confused as to who's actually right and wrong.

So I'm sorry if this seems like a pretty dumb question but I just want to be sure that I haven't been doing it wrong and to correct my form.