And slight amendment.....
The governing range covers around 1800 up to max rpm. Correct.
At low rpm, yes it is behaving as a fixed pitch, but because the prop is in a severe underspeed condition, the prop is on the fine pitch stops trying to increase rpm by reducing the propellor torque (ie. smaller bites of the air).
This is true for constant speed propellers, however for full feathering systems not necessarily the case:
This is what the McCauley book says:
"Pitch is changed hydraulically in a single-acting system, using engine oil controlled by the propeller governor to change the pitch of the propeller blades. In constant-speed systems, the pitch is increased with oil pressure. In fullfeathering systems, the pitch is decreased with oil pressure."
On the full feathering McCauley props that were fitted to most Barons counterweights and strong springs try to force the props towards feather.
After a simulated engine failure (either mixture or throttles) the props are windmilling a fairly low RPM. I can't recall exactly but <1,200 RPM.
The full feathering props were designed in the event of an engine failure to go towards course pitch as it reduces drag.
Are there references for that?
I posted one already from a 303 POH I have here. I am sorry I did not keep copies of other POHs from my past.
Although 12" or thereabouts provides realistic simulation to teach OEI procedures, and I bet many instructors use this. It is based more on feel than on fact.
Because the propellers are acting like fixed pitch props at such low power, RPM & MP will vary markedly with speed and altitude
From first hand experience 12" in a Baron seems to be somewhat less than zero thrust.
IMHO 1,400 - 1,500 RPM at VYSE is a better starting point.