so i'm working a mage build that only uses only defined magic projection and has NO regular magic projection. my question is how would that work with maintaining an innate magic shield?

would i pay the zeon cost up front and then use the defined projection for the entire duration its maintained?

I usually allow ruling it so, although it is also possible that spending zeon each time the spell is projected would be more correct. Nevetheless, the wording of Arcana Exxet (at least in its Spanish version) clearly indicates that the additional zeon cost is spent when the spell is cast, not when it's projected. Now, I think this is just for turn maintained shields, but for daily or innately maintained shields it's a HUGE advantage. Anyway, that's just the way we rule it!

thx. i was thinking that was how it would work but it seemed kinda strange.

You should probably ask your GM on that one. That question has been up for debate before, on at least the other forum, if not this one (I don't recall). There is no clear answer, as by the rules, it's how you've read it, but that gives a huge, potentially game-breaking advantage to longer shields, so at least some GM's house rule it to be a per-activation cost.