I used to have a link to a study on 40sw with reducing oal. Pressure DOES NOT react linearly to linear changes in oal. In the study a change from 1.050" to 1.000" increased pressure by (from memory!) nearly double to 125,000psi. Can you say, "kaboom"?
Narurally, it depends on the powder, bullet, crimp, etc, etc.... but outside of the operational space, small changes in a variable like bullet depth can DRASTICALLY change an output like pressure.
I think this is the link ....
http://greent.com/40Page/ammo/40/180gr.htm