Thanks Tim.
Funny thing is, I feel these changes in resistance when doing workouts on Tempus Fugit (which I know isn’t dead flat but it’s pretty close most of the time). In fact the last workout I did on Tempus I increased my TD to 50% and I could sense a difference (inclines felt ever so slightly harder and descents slightly easier, as you would expect in free-ride mode).
ERG seems to be working as it should. Did a workout yesterday and dual-recorded it (Neo versus Assiomas) and the difference was less than 1%.
I also came across this old thread (Resistance changes based on slope despite ERG mode).