VRSCSE2: It is you sir who should revise your FCOMs!
You will see that usually the AEVC is in closed mode in flight (apart from in very hot environments) The change at ~2psi occurs on EVERY flight and is not to do with what you suggest - check the ECAM display the next time you fly. The FCOM gives no clue about this but I suspect it is as others have posted, to do with drainage valves closing under diff. pressure.