I was out today testing my mini TT bar on my road bike with 32spokes wheels. I couldn't make much sense from the power data. I did a 5 laps session at sub threshold. The first lap I saved 40sec from my last week's session at the same power output. I didn't climb the rollers as hard as last week but my HR was overall higher.
Second, third, forth, and the fifth laps show the similar pattern. Faster time. Similar power output and higher HR. Yet, didn't attack the rollers as hard as I did last week.
The only thing I could think of is that I, maybe, spent more time at my sub threshold on the flat and downhill.