The horizontal stab is in the downwash from the wing, so when the wing is lifting, the stab is at a relative angle of attack(negative) to its physical angle, and generates a downward force. this force will change with the amount of lift being generated by the wing

So a high stab is better, but not to high.
Flap deployment can cause all sorts of strange effects.
All this will be compounded by a sensitive CG position.
Bob