I only do walls after the ground has first been prepared
I learned this the hard way after trying to do them for the first time (pictured below)
https://steamcommunity.com/sharedfiles/filedetails/?id=2516585165

This was the result after i realised you need to flatten everything then raise.
I know it isn't perfect but trust me this wall stops everything early
https://steamcommunity.com/sharedfiles/filedetails/?id=2513431878

With flattening i find that if a spot remains persistently high or low it means you need to pick or raise it respectively then continue with the levelling.

Also it levels the ground to match where you are standing, so i usually get one spot right where i want it then flatten as much around it to that level as i can before moving.

When it comes to stopping "dirt bleed" it takes precise pickaxeing/ground raise, this will come with time as you use these mechanics more.

Hope that helps!