Certainly was a surprise I can assure you, lucky at the time I had the time to wait during the build for the replacement which was appreciably bigger, probably 30-50% in volume. The point you make seems plausible, but had not read of the difference anywhere prior.
Assume the P38 developed in house by LR rather than the D2 with BMW explains the difference in the choice of push on against screw on but seems strange that they didn't make both the same for stock purposes etc.

