Can you explain why you say this? Why does the location of your center of gravity not affect the pressure on your supporting body parts?
It's the center of gravity of the mass between the saddle and handlebars, since these are where the weight is supported. Moving the feet a few inches forward or back relative to them doesn't change that dynamic.
The legs lessen the weight supported, and that upward pressure reduces the total weight that is distributed between the saddle and bars. It also changes the pressure depending on the angle, pushing you back, forward or straight up as the case may be.