Ok, so lets for the moment say that a spring is not on the cards and that rod strength is not an issue (there are ways round that), in theory, just to prove a concept, if I reduced the diameter on part of the rod length at the piston face, will it result in more force? or will everything remain the same since I didn't reduce the diameter of whole rod length?

Does this drawing help to explain what I'm on about?

Double acting cylinder_01.jpg