I have several skills that are fortified, by objects, or profession like mage. But when I go to buy a new spell, it will tell me I do not have enough Magica to use this spell ?? I'm looking at a spell that requires 190 and I have 266 ? I mean it does enlarge the usable pool of magica, just not when casting a larger spell .

It probably just looks at your base amount of Mana as the Fortifications only exist when the item is worn.