That's it, Armageddon Wars, I was going to guess that. I thought that game had a lot of interesting features. Unfortunately, it was a tad expensive.

On Merc Tactics, are there multiple height levels? How is the traversing from one height level to another handled? In Hired Guns usually you had to use a ladder, but there may have been a hidden key for jumping or climbing up the wall? Most of these games cut corners somewhere, unfortunately, so sometimes the A.I. knows how to handle height levels, and sometimes it doesn't.