I've been thinking about this; Nick, are you aware of this? Granted, I'm no expert, but I don't believe I have seen this in other planes.
It's not a turboprop (maybe that's the issue, I know MSFS isn't great at those), but I adjust RPM in the DC-6 constantly, and I'm always getting the speeds given in the power charts, but I am adjusting both speed and power, unlike the TBM where the TQ increases as I reduce RPM.
I haven't flown the Arrows in too long to comment on how the constant speed prop works there.