Could placing a fan jet further in front and closer to the wing create undesired pitch motion from its exhaust?
I seriously doubt the engine exhaust hits the horizontal stabilizer except possibly when fully stalled. Otherwise, the wing downwash follows approximately the extended chordline and takes the engine with it safely below the horizontal stabilizer, which is significantly higher than the wing.

The one thing I've seen mentioned was change in the centre of gravity generally decreasing the longitudinal stability—which is most pronounced near stall, because the centre of pressure moves slightly forward with increasing angle of attack (until stall, where it moves abruptly aft all the way to midchord).

The other possible effect is that the cowling generates vortices—possibly with help of vortex generators needed to avoid stagnation in the gap between the wing and the engine—that go over the wing at high angle of attack and increase the suction peak near the leading edge and making the forward shift of centre of pressure more pronounced.

The only point regarding tail I've read is that it is not large enough to allow moving the allowable range of centre of gravity forward to improve the stability ‘naturally’.