Here is a possible answer
IF the CG is constant then the TOTAL tailplane down force must be the same .
however - the tailplane drag may change withoutchanging the downforce
SO- change incidence of horizontal tailplane and then retrim elevator to achieve original trim.
Tho some of the old school guys will likely doubt it - you can steer a model by simply changing drag
also - if you look at latest aerobatic setups for indoor flying - you may see angled plates on the elevators tipped inward to add drag -AT THE REAR
this moves the fore -aft center of drag rearward - (obviously) Sorry no charts no math - but fly the plane and you will see that moving drag rearward DOES change handling.
I suspect this is what the incidence change on the racer is doing
Ihave a house ful of various setups which don't fit the "std' arrangments - mostly foam stuff but the proof is in the pudding and these little buggers allow for quick mods and the resultant effects can be easily checked - some work- some donts butth results are easy to duplicate or replicate.