Alright, after some more investigation, I have at least a partial answer. I’m
working on an airplane for which I have numerous iterations of the flight
model. In looking at a previous iteration, I found that although the lift on
the horizontal stabilizer was still not negative even at the forward cg limit,
at least the variation of drag with cg position was correct. That is, drag
decreased as the cg position moved aft. One of the changes between the flight
models was to reduce the elevator_lift_coef parameter, described as the
slope of the elevator lift curve. Changing this parameter back to the default
(by removing it) resulted in the correct variation of drag with cg position. I
have had other issues with this parameter and the elevator/horizontal as
described in these questions: https://devsupport.flightsimulator.com/t/4671
and https://devsupport.flightsimulator.com/t/4447. (Note: Although the
default Asobo A320neo flight model cfg file does not include the
elevator_lift_coef parameter, it has the elevator effectiveness parameter
set to 0.75, which I believe does effectively the same thing as reducing the
elevator lift curve slope.) I am finding it difficult to find the right
combinations of parameters to reduce the pitch sensitivity (which seems to be
a common issue in MSFS) without messing up something else, and the SDK does
not seem very helpful to me in that regard.