I use Blu-Tac. Perhaps that putty is better. I am well aware of all the issues you mention but awareness is not the same thing as success. Pardon me if that sounds a bit snippy. It can be frustrating to do all the things one is supposed to do and still not achieve the desired result.
One thing I find interesting is that some paints are better than others for coverage. I call them ‘good paints’ and ‘bad paints’. Good paints cover very well in thin layers. Bad paints are usually watery and do not cover. My current hypothesis is that this is related to pigment size, pigment density, and chemical attributes of pigment grains.
Earlier this month, I executed a somewhat complicated, hard edge camouflage pattern on a Jagdpanzer 38. Vallejo Panzer Chocolate Brown worked quite well and mostly left good edges. Vallejo Panzer Olive Green misbehaved in every possible way and left many tattered edges. The former is an example of a ‘good paint’ while the latter is a ‘bad paint’.