What is the CG of the aircraft? Perhaps there is an issue there that might affect the necessary lift from each head.....which might change that ratio.
I am purely guessing on this.....but it would seem "airspeed" would have to be a function of pitch angle of the airframe as you have no way to level the fuselage by using speed trims.
Would reducing the sensitivity of the collective inputs make the aircraft less sensitive and perhaps more stable?
I bet it is a thrill trying to work all this out!
There was a really sharp guy that built a Huey helicopter complete with turbine engine that did some flights where Huey 509 was based several years.
I will send you a PM on a way to get in touch with him.....hopefully.