I think the lift from the engine nacelles is the problem, with pitching moment even worse because the engines are further forward.
I would also think that stab downforce needed to be increased to counteract the moment arm produced by the fwd position of the engines, but since the flight deck stab trim indication is similar to the NG this must have been done by a hidden re calibration of the stab incidence. This would contribute to a change in pitch characteristics due to the required increased downforce.