Pretty sure MUL's custom cards calculate TMM based on inches.
So you can't use proper movement values for hexes and retain correct TMM.
Do you really need proper hex movement value in the cards? It is half of listed movement after all, should be simple to remember. (Or just say the rule is "two points of movement per hex".)
If you really need, there's one thing you can do: Specials field allows free form, so you could add "Hex MP [value]" there.