I agree with Lozmoid. Of course, a battleship is not going to be on the same scale as a tank, an infantry or a bomber. That would be impossible to play this game. However, units within the same category (vehicles, air units, naval vessels) should be somewhat close to scale.
I also understand that it won’t be 100% perfectly to scale also, like cminke mentioned about battleships vs destroyers and submarines. Yes, in real life a battleship was much larger than a destroyer or submarine and in the A&A world, if subs and destroyers were in actual scale to battleships, they would be like straight pins and barely an inch or less in length. That would be impossible to play with. However, even in the A&A world, a battleship is bigger than a cruiser, a cruiser is bigger than a destroyer, a destroyer is bigger than a submarine.
It’s the same with air units. Strategic bombers are largest, tactical bombers are mid size and fighters are the smallest. It’s probably not in perfect scale, but they are still noticably different in size for easy recognition and works for our gaming purposes.
Vehicles should also follow this rule. A truck or a half-track should NOT be as large as a King Tiger tank. That would look absurd. Making them this big is dangerously moving into Table Tactics territory (with Shermans the same size as Tigers, etc.). All the land units, NOT including infantry or artillery, should be at least close to proper scale.
On a personal note, I LIKE the trucks from BOTB and the half-tracks from Europe 40. I think they make the board look better and I like that they are smaller than tanks, even the light Japanese and Italian tanks. You really need to reconsider this FMG.