As you say, the radar detectors are not historically accurate.
Metox and Tunis are, in fact, deliberately *reduced* in range to compensate for the earth's curvature, so that radar on warships is seen less easily. Air-borne radar ought to be detected at much longer ranges.
It is, however, true that we have not modelled the unreliability of these radar detectors. We can't think how best to do this.
Be grateful that the detectors are effective. I can't think of a single real U-boat commander who complained to BdU that the radar detection was too long, and could it be reduced?
Stiebler.
NYGM Tonnage War Mod - Leading Edge Realism