First a disclaimer: There are experts here who know exactly how things work (I only have observations to contribute at this point).
I noticed the same with mine (different system, but similar physical properties). The IMA System was called-upon less frequently, more engine RPM was required through the CVT, and I heard the pack's rear cooling fan for the first time. It had been parked outdoors on a 100+ degree day and the vehicle just labored the entire 45-minute, 50/50 city/highway route (and continued to do so every afternoon during the hottest days, which have been many).
A big hit in FE was noted and the battery depleted faster on a well-tested route, with same traffic conditions / driving style, similar wind, with the variable of being hotter and more humid. I think the temperature may effect the way the pack can handle rapid charging through regen braking (which equals heat) and likely feels like fading, requiring more pedal/hydraulics.
The cooling fan took me by surprise -- it was based on whether I had the HVAC system on, so it may use part of the A/C or blower(???). I noticed it while backing in the garage and powered-down the A/C as usual to get ready for next startup (just being curious, I switched the air back on and the pack cooler was noticeably loud -- earlier, I didn't hear it over music, traffic, etc). I make it a habit to keep the vent completely uncovered by the seat belt and direct some cool air back there.
Lately, I have parked the Insight, and have used the Integra when I don't need the child seat. I have a nagging concern that the batt pack wears faster in these conditions. Again, just a conjecture...
RH77