Ahhhhhhhhh I see.
I think the solution here is not that. I would argue for terrain extension/ raising. Forcing a camera to angle down at the edges feels bad- it gives more of a loss of control feeling than a bounding box, which does do that, this would just make it worse.
Now you CAN do what you’re implying… however the math would get unwieldy pretty fast versus just making the terrain higher. Alternatively, you could set the camera’s maximum Z lower, as well. Cities Skylines is okay with a high Z position because the terrain goes out WAYYYYYY far. But if you look at most other RTS’s they have a definite “Zooming out beyond here takes the player out of the action” point. You need to figure out what that point is, THEN adjust your crater edges to make sure they’re high enough and the X/Y position limitations are enough. It’s gonna take a little tuning, but I can guarantee it’ll be easier than the math you’re wanting.