Just been running a few test with a iPhone 6 running as wifi WAN on a HD4.
Noticed that file transfer was pretty constantly limited to 2 Mbps which I had not noticed in the past. (running a SpeedTest on the iPhone was giving results of 15 Mbps)
Plugged it in to charge and the speed shot up to 9 Mbps immediately. Left it for a few minutes then unplugged the USB cable and the speed went back down to 2 Mbps.
I will be testing this in a different location soon!
I must note that the iPhone remained in the same position throughout the testing
First column - no USB charger2-4 - USB charger in
5th column - no USB charger
6th column - USB charger back in