Power source

Normally use the Neo with no power source plugged in, but when I have plugged it in the power seems slightly more responsive, or perhaps its just my imagination. I am racing TT events on Zwift on flattish routes and wondered if there was any hard evidence (has any tested it) that you do get better rolling speed with a power source as every course has some down hill even if only slight?

Appreciate the easiest solution is to just pedal harder, and I promise you I am, but in TT's every second counts. If I can optimise the Neo performance (as well as my own) and be confident I am not loosing any advantage over other riders using Neo's that would be nice to know.