I'm thinking more and more that one of the big keys to the tactical layer on classic is the use of the AI's limited vision. I'm finding that when I have some High cover that blocks vision, I'll sneak a guy, and the AI often won't engage that guy/ pretends it doesn't exist, so I can often get easy flanks/overwatch shots. I can often put a guy on the side of a big truck, peek out, and if enemies come to say hi, I'll retreat where they can't see me, and often they'll ignore that unit entirely, giving me some easy flanks, or I can pull them back far enough to run into an overwatch cluster fuck.