(I still maintain the designers of HG 1 made an error with the drive % tables and that's the real reason for the drive size disconnect.)
I can't tell where the error is (if we assume there is one), but it has always beated me why in Bk2 jump drives were (to achieve the same number) more massive than maneuver ones, and in HG this was reversed.
To have a 1000 dton ship with J4 M4, in Bk2 you need to devote 105 dtons to JD, 39 to MD and 61 to PP, while in HG you need 50 dton for JD, 110 to MD and 40-120 (depending on TL) to PP (totals are 205 dton in Bk2 and 200-280 in HG, so largely affecting its performance too).