Update. New, interesting data after reading the thread on big vs. small ring (Big vs Small Chainring - Same Power (ERG Mode Gearing) - #241 by mcneese.chad).
I have been doing all my TrainerRoad ERG riding in the big ring. After reading that thread, I decided to try doing today’s workout (Antelope) in the small ring, except for the last interval, which I did in the big ring.
Well, guess what? The Kickr and Stages power levels seemed to match when doing the workout in the small ring. The big mismatch came back in the last interval, where I switched back to the big ring. I have uploaded the TrainerRoad file (Power match Stages power), Zwift file (Kickr power), and Wahoo Elemnt file (Stage power) for this workout.
Big ring was 53-14 or -15 and small ring was 39-17 or -19.