Is medium difficulty possible in the current version? I've tried a fair few openings now and there doesn't seem to be a way to balance firepower with getting to mineral patches. The starting position is pretty far removed from land worth grabbing.
About the best I could get to was wave 12, at which point I didn't have half the stopping power to counter one tank, let alone two. Even that much was accomplished in no small part because a good deal of enemies targeted a lone bit of wall.