I too am almost 6'3", with a 36-37" sleeve. In a heavy winter parka I shoot 14 3/4, but use a slip on pad to take that up to 15 1/4+ for light clothing.

An old, crude indication of LOP is to hold the gun with your strong hand, finger on the (front) trigger as if to pull it, with the butt against the inside of your strong arm folded to 90 degrees. If the butt just touches the bottom of your bicep, you're off to a good, approximate start.

Fred