I don't know about the Chiaki part, but the Quadstick + Vigembus is delivering a variable value for R2 to the Dual Shock 4 emulation. You can check this with
https://test.quadstick.com and apply variable pressure to the left or right trigger outputs, L2/R2, and observe the values change on the screen with puff pressure.
R2 is B7 on the "Wireless Controller" test display. The number and the shading on the trigger varies with pressure when using "normal" between the output and input:
| right_2 | normal | mp_right_puff |
You can use the increment value function to hold the trigger half-way.
| right_2 | increment_value 50 | mp_right_puff |
The value will be latched at 50% with one puff. It will go to 100% with the second puff.
Use another input to clear the latch with a force off or normal function, or switch to a different mode that does not latch the R2 output.
If you are using R2 in the config "normally" in the mode sheet, use a seldom used input, like right+center soft, to set the latch, then you can clear the latch by just quickly reverting to your "normal" R2 controlling input.