You're measuring unloaded resting voltage. Your full load voltage drop with that setup at that gearing will be extreme - I'm surprised you're not tickling the LVC if that is your end voltage. For example, at the end of a 6 minute race run, a 2s pack in my 1/10th mod buggy carpet car might read around 3.75v/cell resting but the HW system will report a min. pack voltage of 5.3 total (my LVC is set at 5.1v/pack) during the last run - that's 2.65v/cell under load and you should be pushing your packs harder.

In other words, for what you are doing, actually, nothing seems unusual even if you are only doing a limited number of full pulls in that time.