As well as being shaped differently, the fairing was strengthened, because of this problem:-

Initially, as modification 1546, it was designed for the XVIe, and 2nd. TAF airframes, with .5" Brownings, were given priority; eventually its application was widened to include the XIV, XVIII, 21 & 22. Leaflets were issued, so Squadrons were deemed perfectly capable of doing the work; note that it wasn't ratified until December 1944, so aircraft, before that date, would not carry it.
Edgar