Moteino M0 self heating BME280 breakout above ambient

[Stereodude]

So I soldered my BME280 breakout board directly to the M0 as intended/designed and shown in the product photo for the breakout board, and made a quick and dirty sketch to check for functionality before trying to send the data over the RFM69 radio, but I noticed that the temperature readings from it were above ambient.  I tracked down the cause and discovered that the BME280 seems to be warmed by about 4-5 degrees F above ambient by the circuitry on the M0 board itself.  My IR thermometer confirms the PCB temperature around the BME280 is warmer than ambient and that the BME280 is accurately reporting the temperature of its board.  The board's voltage regulator is on the other side of the board and the M0 is pulling current all the time since I don't have the M0 in standby (to keep the USB port and the Serial Monitor alive).

Do I need to put an airgap between the boards or mount the BME280 breakout differently so that there is minimal thermal contact between the two, or will the problem largely go away when the M0 is in standby most of the time instead of running and the average current consumption is much lower?  I plan to make a remotely mounted temperature, pressure, humidity, & ambient light level sensor with the M0 sending the data back to a gateway.

[Stereodude]

I will answer my own question...

Once I got everything working and switched the M0 to use standby and only wake every 30 seconds to send a reading over the RFM69 transceiver and go back into standby there's no discernible heating of the sensor from the board.

[Felix]

I would totally expect this behavior as the BME280 is a highly sensitive sensor.
When you mate them board to board, it's appropriate to use the setup in a sleep mode, where the mote only periodically wakes to poll the sensor, transmit data, and go back to sleep. In such a scenario I would expect there be no significant self heating during that very short wake to poll period.
If the board is on permanently then it would be appropriate to add an air gap by mating using headers.