I'm think that might be coincidence or a stronger transmitter on a plane. They can range from 20w up to 200w. According to contacts at uAvionix, the pingBuddy runs optimally on less than 200mAh. We tested this at OSH, seeing traffic 20+ miles away with it plugged into the side of the iFly 740, low power USB. This was while on the ground in our rental home and at the show.
According to them, there is no performance improvement with 1, 2.1 or 2.4 amp powers. Makes me wonder if one of your batteries was noisier than the other. Or if they were tested at different times, maybe the atmosphere was ripe for signal transmission. Hard to say.
I'm just passing along the power details from the ping guys. I've got a pretty good working relationship with them.