How to target the low part of an object to add dirt?

[lookdev]

Just the low part, the closest to the ground needs to have that dirt. I can't position it there.
I've tried black mask, add fill, greyscale, dirt4 but it's everywhere
I've tried black mask, add generator, dirt, still everywhere

What parameter would help target the low parts?

[volker]

There is a smart mask ground dirt preset in the shelf -> smart masks that you can use (put your dirt material into a group, and drag-and-drop the ground dirt preset onto the group). Adjust the mask editor values (position gradient balance ect) to adjust the height/intensity of the dirt.

You need to bake the mesh maps (position map ect) for your object first of course.

[lookdev]

Thanks

[bwcszark]

This series https://academy.allegorithmic.com/courses/getting-started-with-substance-painter-2018/youtube-IGGQl9kVB1M of tutorials show how to do that but I can't remember which part it is in.

[CodeRunner]

You can also use the 3D gradient tool to do something with a specific area of your mesh. Especially if you use it as a mask opacity filter. It's a bit wonky to use because you have to set x,y,z coordinates into the color fields, which is very unintuitive, but after you get past that, it's a handy tool.