dick Hanson,
Actually the correct way of describing it is the propeller is that it uses the pressure differences to move forward, not the increased pressure behind it. Exactly like you stated, same principle as of a wing. A wing is having a lower pressure on the top swich sucks it up....
Ofcourse it is the pressure differance that is making the airfoil to work. Messing up the air behind the prop will affect its performance.
I am a professional pilot flying full-scale.