Previously I wrote...
As delivered the, servo mounting flange on the standard horizontal plenum sump has a diameter sized for an RSA-5 servo. The much larger FM200 will bolt on with an adapter, but the small sump inlet is still there, choking the flow.
Picture worth 1000 words...during a recent inspection I shot this photo down the throat of the FM-200. The gold constriction at the rear is the adapter, reducing the FM-200's diameter to the sump plenum inlet diameter.
The FM-150 was not available back in 2007, thus the 200 on an adapter.
Much of the of throttle plate angle change near WOT does nothing significant.