Fairies Casting Disguise Self

So I was wondering... If I were to make a 1 foot tall fairy that can cast the spell Disguise Self with the explicit purpose of making itself smaller, could I make it visually shrink to the point that no one can see it any more? 

You mean the UA Fairy race? They are Small size category and being 1 ft tall would be Tiny size category. So that would be a non-starter to begin with.

As for whether it would work on a creature 1ft tall or less. I wouldn't say so. The disguise still needs to be a visible illusion - otherwise you're just casting Invisibility at 1 level lower.

Well the problem with it being bigger than 1 foot is I can't see the reason why they would justify the race trait that says, "You can squeeze through a space as narrow as 1 inch wide". Unless you are roughly the size of a barbie doll and even then the size may be too big... 

In terms of sizes isn't it that a small creature can control a 5 by 5 ft area. With the ability to fly I figure a fairy would be able control that area fairly well depending on the class.