Today at an event our team was told they could not place a rubber band under a wheel that is attached to an anti-tip. They were told it violated the rules, but know one could tell them what rule. The person who made this ruling said a robot must be able to be picked up and moved without expanding outside the area 18 inch cube. They also stated the foam tiles are a field element and cannot be used to restrain a robot. the only rule that I found that comes close to this is R4c. We can redesign our robot, but would still like to know what rule is being used.
Please note that both methods of sizing do not all the robot to be restrained in all directions EXCEPT in the direction of the flat surace/tiles. Thuswhat you have described would be legal. If we did not allow Robots to be restrained by the ground, it would become nearly impossible to inspect for size.