No! INT shouldn't affect damage more if stances are up, if yes then it's not working properly.
I thought that you have tested it and made it clear that Mage stats do no affect stances because stances are not magical attacks.

I am always parsing my damage against 50 level Amaljaa, I will not use stances because they are resistant to fire but I'll say it again, INT shouldn't affect damage more than STR.