How to avoid that paint "climbs up" against the tape used to avoid spraying certain areas of the model (eg with camouflage).

I think your asking how to avoid paint buildup on your masking tape edge.....

I did a german figher a while back in three tone camo and I just airbrushed it in thin coats and sprayed across the tape away from the edge....didn't push the stream of paint across the edge of the tape....

used tamiya tape for this project also...

example

yes, that's exactly what I mean. I'll try the way that you hav described it.

Thanks a lot for the tip!!!

also for smaller masked off spots i just sprayed thin coats straight onto the surface.. trying not to get paint build up on the taped area's..

did have a slight ridge on one spot on that model and just hit it lightly with a polishing stick took care of it.

spraying the paint on in thin coats is the main thing...

I'd suggest practiceing first on something non-critical..

I used a 2 liter plastic soda bottle. sprayed a base color.. then masked off some spots to practice my airbrushing and masking techniques..

Here's a little thing I like to do, once my tape is laid down i'll spray (airbrush) a clear over the tapes edges. This will seal the tapes edeg. If I'm using gloss it'll be a gloss coat and dull coat for dull paint. Works pretty well.