Incidentally, I have thought of a way to have multi-tile bots and exos, Keith, which would be both easy to code and not break pathfinding.
1. Have an entity that draws itself around 3x wider and taller than normal, so that it takes up 5 tiles instead of 1. Visually this is trivial, as you know. However, in reality it still only exists on one tile.
2. When it is checking "can I move into a tile," it says "no" if there is not a ring of empty tiles around the tile being checked. That would handle pathfinding right there.
3. For other enemies doing pathfinding, or the exos, when they check a tile to see if they can move into it, the answer is "no" if one of the larger entiteis is within 1 manhat of them.
4. For shots hitting things, explosions, etc, whenever they hit a tile they see if they are within manhat 1 of any large entities and then hit them. Possibly with an added flag to say that a given large thing can only be hit once by a single attack, but maybe not.
In this way, the entity under the hood is really still one tile, but visually and in many ways functionally it is one tile. Minimally invasive changes, relatively speaking, although certainly there would likely be a lot of related edge cases and bugs for a while. It's an idea for an expansion at some point, though.