R22 beta II manifold pressure

I have found that he manifold pressure gauge on the betaII does not behave like the real beta II. If one increases collective the gauge goes to about the right place, but it does not stay there; it drifts down to between 14 and 16. For example, to climb at 500 ft/min do 60 kts one should see a manifold pressure of about 22. One does not. This means that controling the collective expecially during landing and take of (i.e., hovering) is difficult and unrealistic.

Does anyone know of a fix for this or know of an addon beta II that is more realistic.