The AT+TXP and AT+ANT effects will be changed for the US915 in the next release. The current release will subtract the gain from the output power
Under FCC the maximium conducted output allowed is 1 W (30 dBm)
Depending on the number of channels enabled and the datarate used this limit may be 21 or 24 dBm
Antenna gain up to +6 dBi is allowed with 1 W.
Higher than +6 dBi must dial back the conducted power the amount of gain over 6 dBi
The mDot library will use the antenna gain and tx power settings to stay below.