Running away from 4 units is a death sentence. But on the other hand, 6 Imps drain mana very well. Yes, taking health from 1-2 units of Lepers is not a good idea because it's not efficient. I took a step back to the Fortress; you're right. But nevertheless, using shortcuts, you can take the Altar on the first turn, eliminate the Fairies, upgrade the Sawmill, and get armor using this normal tactic without heavy save-loading. It's a pity about the 36 skeletons. I didn't lose any Imps. Maybe I should try to clear the battlefield of Fairies? :)
By the way, what did you choose for the upgrade? :) I chose health; I think it will be useful.