AUX output always neutral on Pixhawk?

Hi there, I’m having a problem with AUX output using Pixhawk 4. I would like to see a value different from 1500 on AUX 1, but it seems I’m doing something wrong. I’m manually publishing values on topic actuator_controls_3 by means of a custom module (publishing works properly checking it with listener actuator_controls_3), but the output is always stuck at 1500. In principle, publishing on control group 3 number 5 (so the 6th element) should convert the input (between -1 and 1) into a value between 1000 and 2000 on actuator_outputs, right?

The airframe is the original 6001, therefore the mixer is pass.aux.mix:

AUX1 channel (select RC channel with RC_MAP_AUX1 param)
M: 1
S: 3 5 10000 10000 0 -10000 10000

Is there any documentation about the relationship between actuator_controls and actuator_outputs? How is the mixer able to understand that actuator_controls_3[5] should be mapped with AUX1?

(I’m only connecting Pixhawk 4 to the PC without any other component)