Having Trouble Fighting Mages Options

[Castle]

This is my first time playing through IA; great mod! Much more challenging than the original game (perhaps too much for me, I fear), which is a nice change.

Mages, though, are a problem. Their many-layered protections were annoying enough in the original; I'm finding them impossible now. Improved Invisibility + SI: Divination makes them impossible to target with breach, and my mages are too low level for dispel magic to do anything.

Furthermore, they seem to have ridiculous ACs: Korgan (with a THAC0 of 3) is missing on a 17! Melee enemies certainly don't have armor that effective.

Any advice?

[Hoppy]

Maybe thieves could have a special ability to detect things like AC, protections from items, and maybe spells since their other (trap) powers are ineffective. This ability increases by level and can be avoided by non-detection or protection from magic so that it does not get overly exploited as cheesy or overpowered. Making them more like spies for reconnaissance. That just fits more in to tactical evaluation techniques like the "Art of War."