I am also in the small chainring 99% of the time.
That only changes for the 5s sprints.
But that can depend also on your sprint power/cadence combo.
If you are at the same power, it should not matter to be in big chainring lower level Vs small chainring higher level.
Only difference will be flywheel speed as it has been mentioned.
It is said that higher flywheel are better for sustained efforts, as it can help to smooth out pedal stroke.
Lower speeds with higher resistance will react more to small accelerations/drops.
There is also merit in changing levels during the test, as you can fall in a “gear gap”, as in for the power you can put out, cadence is slightly too high in one gear, and slightly too low on the next.
This used to happen to me on the MAP period, so cadence too high my HR would explode, next gear cadence too low, my legs were toast for the 20min part.
But that was on a fluid trainer with a very steep power curve.
I now have a KICKR and play a bit with the levels during the test to get cadence right where I want it.
I set my BOLT to control the KICKR and systm app is just recording, so I can adjust levels/gradient easily on the bike. (My computer is far from the bike connected to a wall TV).