Hi, i am fighting exactly the same RSSI puzzle.
I have Dragonlink v3 though.
In the end, after massive hair loss, i've installed newest Dronin GCS, which has by default RSSI channel assignment (PPM, PWM, sBus, etc.).
For minomOsd i flashed MWOSD 1.6.
Issue solved.
I don't understand why LibrePilot doesn't support that.