Have you noticed that the problem becomes strange when the wing is completely covered by the fuel tank? The horizontal stabilizer of some airplanes only has the function of flaps, cannot control the nose pitch, or has both functions? The aerodynamics of this game, to be honest, is very poor. I very much hope that you can move over the aerodynamic code of simpleplanes, because this is really bad.
This is an example of a horizontal stabilizer with flap function
https://www.simplerockets.com/c/ylw1Ma/Failed-product