I did not attempt to fly it with Outerkp = 12 . Playing with TxPID I just checked on the bench how the cyclic was reacting decided I could play "in the air" with a 2-6 range in TxPID. My actuator outputs do use 100% mix as I've got an old fashioned cyclic with one servo for roll and one for pitch (no mix). With the same outerkp I've got much more throw on pitch than on Roll (only difference being the PIDs between these two axes).
I rather doubt I've got the skills to elegantly modify the integrator code... I was considering modifying the mixer output so as to combine 100% Roll + 50% Accessory3 on Actuator2 (accessory3 being feed by the transmitter). Assuming lots of transmitter expo on accessory 3, Roll command would control Actuator2 up to 25% stick travel, beyond 25% Accessory3 would gradually override the flight controller.
Any chance the flight controller does not get totally upset by this crude approach?