As a fellow migraineur, I feel compelled to point out that the quest for triggers and root causes is probably never going to end. The way I see it, the migraine "bucket" slowly fills up, and the final trigger is simply the drop that makes it run over.
I can suggest the research papers by Markus Dahlem for some in depth modern takes on migraine.
It's definitely bucket-like for me, and I can attest meditation empties it. Whenever I stop meditating, mental busyness and subconscious anxiety slowly build up. Half hour a day is enough to keep it away. I just keep bringing my attention back to the breath, trying to feel into the physiological need to breathe (which is usually occluded or distorted by mental activity). Whenever I feel I am actively holding to some tension, I allow myself to release it. That's all in terms of instructions, and for me it works wonders. I look at it as the equivalent of flossing for the brain ;)
Maybe they can find out what empties the bucket.
E.g. meditation, yoga, ...