Regardin the fact, that surfaces themselves deal hardly any damage, except if you can blow them up, I would say 75% damage increase would be far to much. Also each skill would need and estimate for created surface in their description? Also most surfaces don't deal damage at all: ice/water/blood. And how would it work for air? Air itself does not create surfaces, but it affects 'surfaces' if they are water, blood or steam.
Numbers can be tweaked, maybe a 40% damage boost? (25% would be too low.)
As for Air, hmmm... well since air does not CREATE surfaces, then naturally Air is neither affected by the penalty nor gains anything from the bonus.
