If you are completely engulfed in air you're like a diver underwater achieving neutral buoyancy, the same kind of thing as a perfectly balanced balloon. So you're floating in air rather than on air.
Huh? Half the article talks about how they maintain buoyancy while submerged and why that's important.
You don't need a boundary, and it wouldn't help you if you did. You still need to displace the same amount of air.
The only way on/in makes a difference is if you have some way to prevent the fluid from going around you. You'd have to be tightly jammed inside a tube for that.