This was something that was bugging me while I was setting up a small mission, with the new armored vehicles. I had 2 AMV-7s and 1 Hunter, with the AMV-7's both in the front. The second AMV was blocking the only exit from the compound, and all 3 vehicles was placed without formation.
When the waypoint started, the first AMV moved a bit forward, while the second didn't move at all, and the Hunter trying to cut through, though it didn't work. When I placed them all to be in formation from the start, I noticed that the Hunter was placed in the middle of the 2 AMV-7s, which was also the position it was trying to achieve before. So basically, the convoy wont move until they're in the proper formation, and does nothing to help other vehicles achieve their position.