Shogun,
In years gone by when I had a Testor's A220 airbrush (not much more controllable than a rattle can), I had tried essentially the method you have described, and got inconsistent results, for exactly the reason that Aaron suggested, parts of the mask lifted more than others.
I got better results with Klem's method. Because the edges are all fastened down, the softness of the edge transistion is pretty much dependant on how far off the surface the mask is.
On the other hand, after updgrading to a Paasche H, I easily I did a 1/35 tank camo freehand. As Ajlafleche says, get the tip in close and carefully spray.