Vehicle size question

[Eclipsetech]

It has to be in the ai files somewhere but damned if I can find it. The 3 - 2 thing is right. A nuclear engine I generates 6 movement points. 2 engines max = 12 movement points. 3 engines per move is actually points per move so 12/3 = 4 space movement. Its a slight variation of proportions mod. I may have to start over from proportions mod as a base and make one change at a time till i figure out the problem.