Ok, Moritori, one thing you have to consider is the nature of the vehicle. Lets go through each type.
1. Wheeled Vehicles - wheeled vehicles have trouble moving in formations because they are config'd to "prefer roads", meaning if they can, they will allways take and follow roads to get to their destination, if they get to a point where no road can take them any closer to their destination, they will leave it, but when they leave the roads they have a hard time even driving in a straight line, much less in formation.
2. Trached Vehicles - tracked vehicles are excellent at moving in formation, since they don't really care where they drive (unless turned out/set to safe mode - where they prefer roads), however you have to consider the differences in max and cruising speeds for the different types of vehicles in the formation.
3. Rotary-wing Aircraft - the worst at moving in formation, helicopters just can't do it. The reason is because of the delay in a helicopter's movement, basically when the lead chopper starts to move forward, it first pitches forward to get forward thrust, and the rest won't follow it until it starts moving, and then they will have to pitch forward, and will end up way behind the lead chopper.
4. Fixed-wing Aircraft - given the behavior of helicopter formations, planes are suprisingly good at flying in formation. There is only a slight delay in following aircraft to mimic the lead aircrafts movement, but alot better than helicopters since planes usualy have very responsive controls.