TYPE:"cm:content" AND PATH:"/app:company_home/st:sites/cm:site1//*//MYCUSTOMFOLDERNAME//*"
That query now is running correctly.
But I've another problem that probably can't be solved.
MYCUSTOMFOLDERNAME is composed like this -> "[id.id.id] FolderName" so I was trying to replace that [id.id.id] with another * like below:
TYPE:"cm:content" AND PATH:"/app:company_home/st:sites/cm:site1//*/*MYCUSTOMFOLDERNAME//*"
This is the real case where I have no results.
Anyway, I know that the ANCESTOR is the best approach if we prioritize our server performance but my query will be necessary only for statistics purposes, so it will be run only few times for year and manually by an admin user.