Thanks Ken 
Hmmm...good one. Got me there - a wee bit.
Umm...
Ahhh...
Honestly, pick the category you want to enter - Armor or Air - and then see how things go. If I were you I'd take the diorama route.
In the future the categories will expand / get refined. This is only year 2 and therefore we are doing our best to keep things simple....to avoid......confusion. :-X