Didn't want to create work for you Rupert! As I said, I've used your formula since the 1990s. For consistencies sake, I think you should use it with all KE warheads, especially however those high-tech mass drivers which otherwise go through mountains.
ME PV
12+ (ME^(1/2)) x 14
<12 (ME^(1/2)) x 15 (but never higher than 48)
< 9 (ME^(1/2)) x 16 (but never higher than 45)
< 7 (ME^(1/2)) x 17.5 (but never higher than 43)
< 5 (ME^(1/2)) x 18 (but never higher than 35)
< 1.5 (ME^(1/2)) x 10 (but never higher than 12)
< 1 ME x 12 (but never higher than 10)
< 0.5 ME x 16 (but never higher than 6)
< 0.3 ME x 22 (but never higher than 5)
The other fix for mass drivers is to read point A.2. on page 110 of FF&S Mark 1 Mod as actually meaning "Muzzle velocity at tech level 8 is [UP TO] 3000 metres per second..." thus making it clear that the muzzle velocity figures are the max available but not the only values that can be used at each tech level.
And of course use the correct range formula from the official errata.