It’s likely that the Spectral Mind is considered to be your location for the entire duration of the spell.
First, let’s look at the full relevant text of the Manifest Mind ability:
Whenever you cast a wizard spell on your turn, you can cast it as if you were in the spectral mind’s space, instead of your own, using its senses. You can do so a number of times per day equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
As a bonus action, you can cause the spectral mind to hover up to 30 feet to an unoccupied space that you or it can see. It can pass through creatures but not objects.
The Manifest Mind feature says that you can treat the Minds space as your own whenever you cast a spell. I don’t see a clause stating that the spell snaps back to your true location after it’s been cast, nor do you have the option of doing so even if you wanted to. It appears that, once cast, the spell is locked in to treating the mind as the source for the duration.
This means that the Mind must stay within 30 feet of the target, and should the target ever have full cover from the mind, the spell is broken, even if the target is within 30 feet of you, and not behind full cover.