This is very interesting research @rberkelm! One key piece of data that is missing though is whether you’re connecting to the same tower and same tower antenna with each test. Can you try capturing a trace log (documented here) before the Notecard establishes its initial connection so we can look at the band, channel, carrier mcc/mnc/TAC/cellid, and access technology (GSM vs LTE vs 3G) used for each test case.
Thanks!