Chancel Aleph

This Gift will still allow Masks to know when others are coming near him, since the place where they are won't contain the Estate of Others, right?

Yes, since you can still detect the presence of things that aren't vulnerable to miraculous alteration, since they show a "blank spot."

The main issue with the Gift is that it's built on a level 2 miracle, so Aspect 3 stealth will still technically beat it.

Actually, since it's automatic, wouldn't that be much harder to do?
I mean, wouldn't Masks still know about how there is a blank spot where he should notice the Estate of Others, like say a Nature Spirit or something like that?

EDIT
I mean, the Nature Spirits won't be able to hide from him, so when he notices that he can't tell where they are, he should at least become cautious.

Though I'm not too sure what was wrong with it when he had the L. Div. of Existence instead…

Not if the miracle level they use for "not being seen" is higher than your "I see you" level.

I just thought Existence was troublesome in that it probably counts as a "wide variety of Estates."

The Gift isn't about telling him where things are, though.
The main utility Masks would get from it is the fact that it leaves a "blank" spot for him to notice, an area that he suddenly won't know anything about.
The divination itself isn't as important when compared to the ability to notice when a "blank" shows up on it, indicating an Anchor, Noble or Excrucian-shard.

Even if you act with stealth, you will still leave a blank spot, won't it?
That is, after all, a major part of miraculous beings - they leave blank spots on Divinations.

Otherwise, it'd be easy to find, say, Cneph or find out who gave the Excrucians their first Estate, since they wouldn't leave blanks on Divinations.

In fact, even if they use a miracle, to hide themselves in order to sneak up on him, that also leaves a "blank spot" for him to notice, doesn't it?

And, since nothing short of Imperial Miracles (and Blind Lie, I guess) can alter Masks perceptions or thoughts, he should notice when an area suddenly appears as something he can't know anything about at the moment.

They'd still leave a blank spot; they'd just be hiding it by being very sneaky.

Just like how normal people being stealthy are still visible; they're just taking trouble to make sure you don't see them. It's the same principle. If stealth didn't work this way it would be impossible to do a lot of things that stealth-based characters are going to want to do.

See, I'd say that would require a Gift of some sort, for others not to notice when they can't tell where Nature Spirits are suddenly, by making the Nature Spirits themselves both want to hide as well as capable of doing so.

If nothing else, that would either cost MP or be more than a single CP, for such a Gift.

EDIT
Also, changed the Gift so that it now only tells him that others are coming near him, not their position relative to himself.
And I've increased the Miracle Level to 4 now, as well.