First editions of Alpha Strike had 1" = 15m. So that fit the 2" per hex conversion. However, they have changed that to 7.5m/inch. That gets you incredibly close to accurate 6mm scale. Unfortunately, that means you would need to double movement and/or ranges too.
Personally, I kind of like that idea. Just change the range modifiers to Shord 0, Med +1, Long +2, Extreme +4 and change the ranges to 12"/24"/48"/84". Your blast and strafe templates would need to be doubled as well.
However, if you assume each round is 5 seconds instead of 10 seconds, you don't actually need to modify movement.
Anyway, random thoughts...