The steel will tend to puncture and partially spread the load on the wood. The result will gradually obliterate the underside of the wood until, as Alex said, it might as well not be there, and you're protected by the thin steel.

Unless you go for much thicker steel (or much thicker wood, but I woodn't (heh) recommend it), HDPE might be your next bet. It will have to be fairly thick but it will absorb the impacts to an extent. 6mm HDPE just about holds out Little Hitter, to give you an idea on thickness.