he's got a spell shield up!!!!
you should have breached him TWICE...
i know the trick with the fireshield works, since i too have the latest tactics mod, and about a month ago, i was using sanchu while in windspear hills dungeon, i died very rapidly using sanchu against those djinn with fireshield red...
breach should have brought down the fireshields...after i published my evil methods for taking down undead sola, using chain contingency to punch thru spell immunity divination and improved invisibility, wes had undead sola cast spell shield...so it took 2 ruby rays to take his protections down, followed by breach...wes likes spell shield...