X8 - how to tweak upper vs lower motors thrust?

Hi all,
On big X8 multicopters, I get upper motors to be warmer.
I’m looking for a way to trim power division between upper and lower motors.
I though there was a parameter for that, but don’t find it any more.

If no dedicated param, what would you suggest to do so?
I wonder if changing SERVOx_MAX could change the average power sent to for example upper motors, changing it form 1900 to 1800. The drawback is that I loose some max power on those top motors in case of emergency (lower motor / esc / prop broken).

Thanks for your advice

Nope that is not possible. You will need to change the source code for that

You can do it with a motor mix loaded from scripting.

That motor temperature could depend on other aspects of the tuning.
Please describe the components, minimum and maximum take off weights, plus supply a .bin log file.

Ok thanks for your answers, yes a LUA script will be the clean way to solve our problem. We will maybe try first to change SERVOx_trim to artificially change power curves between top and down props, but not sure it works, maybe output rates will compensate this change.

This octo has centered load, same props and motors up and down.

If you think, the air arriving on down props is already accelerated by top props, so the power sent to top and down props should not be the same. Down props should turn faster on a ideal coax multicopter no?

would using different propeller sizes be an option for you here maybe,

You could try putting smaller propellers on the upper motors to make the draw less current. You could run into some issues regarding the harmonic notch than. Using different propeller sizes can make things difficult since you have two sets of harmonic to filter out. This is possible even though it’s a bit harder to set up.

The other filters should be fine, I would suggest setting the Accel, gyro, and rate filters according to your largest propeller size to begin with if you decide to try different propeller sizes