Need to adjust the Gain

if you have 3 RPi’s (A, B, A+B), the feed to Flightaware will be only from those RPi’s on which you install Piaware data feeder.

However if you have installed Piaware data feeder on RPi A+B, then you will have to turn MLAT off on this RPi. In case you dont turn off MLAT, the Flightaware System will detect merged feed and will disable MLAT

For non-merged RPi’s A & B, you can feed Flightaware with MLAT turned ON.

Yeah i feed both dongles to FA separately and then on one of the 2 computers i have a net-only dump1090 running that combines all the data into one view.

Basically you have your ordinary dump1090-fa and piaware installation on both computers.

Then on the one you want the composite view you add a net-only version of dump1090 and use socat to feed it all the data.