[narwan]

As to size differences there is one important thing you shouldn't forget. There are so many units in this game fo any given general type that it is very easy to put them all next to each other in such a way that each next one is only fractionally larger than the one before it. In other words they are nearly the same size and according to your logic they should have the same size in the game. But that would mean the smallest one in the line would still have the same size as the biggest one in the line! Somewhere along the line arbitrary choices have to be made as to where a size upgrade is put in place, even if this means that two units that are nearly equal in size in real life end up with different sizes in the game. It is an unavoidable abstraction of the game.

Then there's the problem of what to look for in 'size' of a unit. I recall an earlier debate for WW2 units on this same issue where the question was how to relate tank height, width and length into one 'size' factor. The british Valentine for example was significantly lower but much wider than other tanks in that period. How to solve that size wise?
Same with helicopters. Do you look at size of the fuselage and if so at the length or width or height in particular? Do you look at the height of the rotor section or the span of the rotors? How do you weigh all these factors to come to a size factor that is 'real'?
The answer is by judgement call. With which you can agree or disagree.

Narwan