hi! do you know if there is a way to draw on a snapshooted model, and to be at the same “level” (depth?) than the model, without the visible frontier? (i know, there is the alphas brush, but less fluent than the usual brush) ; thank you 
Have you tried the Bump brush or singlelayer Brush ? Also I’d try experimenting with the stroke mode settings
I don’t think if you mean to ‘pick up’ the paint, the way the system is built it always catches on additively to the underlying depth. You could perhaps with layers, painting them individually at the same depth and adjusting the Z location to interpolate but it’s just too cumbersome. The best bet is to use smudge to blend or even out the levels of paint.
I too would like a “bottom catch” to the Z sliders, so that we can continue painting at a certain depth, “in” a certain depth. 
That way, it also would not be a problem running out of paint before finishing an extensive stroke. Either way, use of the smudge brush is mandatory.
-more helpful in this case to turn on zsub I think.
Would it work to set the ZDepth slider in the Picker palette?
No, the zdepth slider currently adds to any existing paint regardless of its depth during its procession.
However, here is an idea I just remembered from Pixolator’s felt collage tutorial - it is possible to use the cylinder 3D tool as a (even topographical alpha) brush to utilize the zdepth picker slider to that effect.
Et un petit coup de “Blur” ne suffit pas pour atténuer tout ça ?
Pour une image fixe of course !
Pilou