For a 1/72 target like that pictured, I would consider doing some form of masking - IF I did not get to where I wanted with that Iwata. (With a little practice and careful paint-thinning and low - ca 5 - 8 psi - AP, you can reliably get lines at or under 1/16 inch wide. Patience!). While "real" sprayed-on camo would appear as the expected soft-edge (overspray in the 1:1 scale), at 1/72, it would be pretty tight-looking - a tiny "fuzzing" along the edges.
PRACTICE with your AB and you'll get where you want to be!
IF you want to explore masking... It is very easy in many cases to make a mask of cheap art "tacky gum" stretched out into a thin sheet and gently pressed onto the subject to delineate your desired pattern. Because the tacky is a 3d sheet, it will have a small "undercut" along your spray-lines and allow a small amount of fuzzing while keeping most of the overspray away.
There are available many "template masks" used by AB folks to create various curves and stuff while controlling overspray - these are available in HobbyLobby and other big crafts stores. They take a little practice, and you need to have your kit propped and mounted at the right angles for you to easily get to areas you want to hit on, but this is actually the way the "pro" AB artists do their thing. (And we are explicitly talking here doing "freehand" and free-form trimming and altering of printed photo images, etc.)
A little practice with any of these, combined with the thinning and low AP and getting closer to your work, are your solutions. Have FAITH! You WILL get to where you want with a little further work and trials!
Bob