I made the same mistake with the P-38 about six years ago (and was mocked mercilessly for it). You're probably looking at indicated, not true. At high altitude, the difference can be very great; in this case, perhaps 30%. If I were you, I'd delete this thread, now.
If that's not the case, then I can't help you. Apparently, however, we do not have the fighter variant of the Mosquito in Aces High II.