A few lines came up in doing these quests (context, I'm wrapping up 6.5 at this time), and it doesn't seem this is going to get addressed. So.. maybe some of you lore nerds has some better rationalizing or maybe it's a translation thing or who knows..
What we know:
Using the Crystal Tower and a pact with Cloud of Darkness, Allag opened a voidgate during their war on Meracydia.
Vrtra tells us his sister, Azdaja, flew through this voidgate during the war (after which it closed, but that's not important [and maybe just coincidence])
Y'shtola informs us that "For a being to navigate the chaos of the rift, with or without form, there must needs be a guiding agent on the other side."
G'raha points out that, in the case of Allag, technologists served to draw voidsent through the gate to the Source.
These points raise an important question: How did Azdaja end up on the Thirteenth? There was no such "guiding agent" to lead her through the rift.
Vrtra (as Varshahn) does point out that travel through a fissure does not require these conditions. Which... I guess is how they explain the whole "we turned Alzadaal's fissure into a gate, allowing us to pass through like a fissure.
Or is this a misinterpretation, and it's more that a "gate" requires a force on both ends to open two-way travel, while natural fissures are just one-way leaks? (and Alzadaal's fissure only required force on Source end for being already present and open on Void end?)
Or is this just the game can't keep "voidgate" and "fissure" straight all the time?
Or is this just a case of "well, she's a dragon, and they're powerful, lots of aether, technically unsundered, hell, she was angry too so maybe dynamis was involved" which seems like an awful lot of leaps to rationalize..