This is actually quite helpful, but at the same time not what I truly am looking for. The bits about tempering seem to be promising, though.
But to summarize my problem again: I'm trying to theorize new techniques for a dnd campaign with FF classes/jobs in a time period where there are no soulstones of summoners lying around nor teachers for the art. The character is self taught entirely. The DM let me get away with some shenanigans for the first egi, but everything else I need to explain aetherically. It's easy for spells, but when it comes to primals we get into this awful problem...
"The allagans did it, so it works. trust me." and things are rarely explained beyond that.
I understand summoning is a bit of a mess when it comes to aetherology mechanics and a lot of it falls into mysticism and 'strength of belief' malarky..
So lets move on to a bombardment of more questions, for now.
So knowing that egis are essentially half of your own aether merged with the taint of a primal and following your will...
...and that you can't add much more aether to empower it or you'll simply die..
What if you gained the aether from another source? From a magnitude of crystals, sacrifices, or if you could somehow draw directly from the lifestream?
If given an unlimited supply of aether would an egi become a proper primal or a supercharged egi? Would it simply explode / pop harmlessly like an overfull balloon?
What truly drives your control over an egi? Is it your will alone? Is it your aether and the fact that the egi is a part of you? Would adding more aether from an outside source cause you to lose control?