If power is sufficient - Up thrust is not required.
The up thrust is just compensation for loss of speed (climbing).
almost all ARFS loose speed climbing -this changes (reduces) trim drag-so the model tends to pitch to belly.
Our own CAPS run 0 upthrust -
We did that H9 73" model w/ZDZ40 when the kit first came out - vertical trim change was not needed .
We also did a number of lighter 80 " models -and the 33% (still have one of those) and the uptrhust thing will show up if you run less power
That is - they pitch to bottom as speed bleeds off.
Bottom line :
If you have enough power to hold constant speed - the thrust problem goes away.