i have an iwata HP-CS, and it likes really thin paint, especially when doing demarcation lines. i also build 1/48, so 1/72 is definetly gonna be tougher to get down right.
the way i do my camo is as follows. i always spray a 50/50 thinning ratio and build up the coats of paint to my liking, and use MM enamels for the most part. when i get the base coat of the camo down(and this being the lightest color in the scheme), i then pencil in very lightly the pattern of the 2nd lightest color of the scheme. when this is to my liking, i again use the 50/50 thinning ratio and spray this on trying to stay with in the pencil lines (i KNEW that kindergarden education would come in handy one day), not paying a whole lot of attention to the quality of the demarcation lines. the idea is to just get all of the participating colors onto the model and really close to the desired color pattern. i do all of this with a 50/50 thinning ratio and using 12-15 psi.
when all this has been done, i then thin the paint even more, drop the pressure to around 8-10psi, and get in really close to the surface of the subject, and begin the long and arduous task of "cleaning" up the demarcation lines. this usually takes about 2-4 good hours, depending on how many colors are in the camo scheme, and how steady the hand is. you'll be in and out of all shceme colors 2 or 3 times during this process too, so thats normal.
with all that said, the people above me hit the nail on the head with the pressure, thinning ratio, and distance from the subject bit. it is a trial and era type deal between a man (or woman) and his airbrush/compressor/paint. hang in there, you'll find the right combo soon enough. the 3:1 ratio at 10psi is not gonna be too preductive, you'll need to thin the paint down some more. good luck friend. later.
PS. i hold my tongue with a slight protrusion out the left corner of my mouth too, kinda like Michael Jordan when he dunkin'.