The stab airfoil sections on the a/c I am familiar with are all symmetrical.

The issue is less prevalent as the distance between the stab and efflux and stab increases, to the point of zero on larger Boomers like the XL. The KC H-stab is a lot closer to the efflux because it's mounted mid vertical stab. The Boomer XL's h-stab is mounted on top of the v-stabs, and it needs NO down thrust. Each of these a/c has the same thrust -vs- Cg configuration, and only the KC needs down thrust.

The thrust line is NOT below the CG. It is, in fact well above it.

It is not a trim-vs- speed issue; the pitch varies wildly with thrust on the models being discussed, and very little with speed.

The trim -vs- speed issues do not apply on "all aircraft". Those with aft CG's plus symmetrical stabs set to zero incidence, the exact configuration of many RC models and some full-size aerobats like the Su-26, are exempt. The Sukhoi, in fact, had NO provision for pitch trim installed.