I’ve always used the same props top and bottom simply because I’ve not been able to find any matching high quality carbon props with different amounts of pitch (I’m currently running T-motor 17 x 5.8" props)
After a long flight, my bottom motors are always stone cold, but the upper motors fairly warm to the touch so there is a huge imbalance in loading going on in my setup.
I remember reading somewhere (can’t find it now) that someone had an X8 with a custom motor mix which sent 10% more power to the lower motors to balance out motor loading when using identical propellers top and bottom. This may well have been on a DJI controller though.
@rmackay9 I wonder if an option to set a per-motor thrust multiplier value (eg between 1 and 1.2) to have the motor mixer send up to 20% additional power to the bottom motors would be viable?
Maybe this would cause problems with flight dynamics but if not it could be a great feature for coaxial rigs.
***Edit - it was a DJI controller: https://www.dronevibes.com/forums/threads/hl-x-flight-times. Of course to prevent output saturation of bottom motors, we would instead need to reduce top motor output rather than increase bottom motor output.