Rc8 setting pass through

Trex 450 clone with kakute f7v1.5 ublox gps frsky running yaapu telemetry.
The swash plate and tail servo are functioning fine as is flight mode and battery voltage.

I have just setup a quad and plane and fly those,
But now with the heli I am having trouble understanding how h_rsc_Mode 1 gets its throttle value from the tx.

As I understand it, rcin8 needs a value to send the slider value to rsc out servo 3
It also needs rcin7 value to be a switch for motor interlock
Then it needs the usual rudder arming (optional)

Ok, by brute force hacking, it seems that 153 is interlock
32 is pass through
31 is emergency stop