What's the actual trigger for Super Saiyan Blue?

[Bulma's Foot Masseur]

Super Saiyan God Super Saiyan/Super Saiyan Blue is said to be attained when one with the power of Super God Saiyan goes...Super Saiyan, but we've seen Goku go regular Super Saiyan since, which by nature is already tapping into Goku's god ki since we've seen him transform when he's already channeling god ki in base. It's believed that Super Saiyan Blue happens when the god power is channeled fully, but I'm still confused about the causation/order of events, especially given how spontaneous the transformation is.

So, the burning question: Is transforming into Super Saiyan required to fully channel the god ki, at which point Super Saiyan Blue happens? Or can it be fully channeled in base form, with Super Saiyan taking on the appearance of Super Saiyan Blue when that god ki quota has already been previously met? What's the actual trigger for fully channeling god ki and what's the actual trigger for becoming Super Saiyan Blue?

[TheUltimateNinja]

It seems to be channeling the power of Super Saiyan and God ki at the same time which results in the form taking on a blue appearance.

[Bulma's Foot Masseur]

True, but isn't Goku always channeling god ki to some extent? Yet can go regular Super Saiyan anyway?

EDIT: I just read the Hit chapter of the manga, and you know, Super Saiyan Red still being an achievable form actually makes this a fair bit easier to deconstruct. It suggests Goku is actually NEVER channeling *all* of his God ki until he changes back into that form, meaning the trigger for Super Saiyan Blue is simply layering Super Saiyan on top of Super Saiyan Red even if they're activated simultaneously.

Previously I had assumed that Super Saiyan God/Red was something Goku was always channeling in base (after "absorbing it" in his fight with Beerus), but if that was the case it wouldn't still be an actual transformation.