The include paths start from the root of the sync. You are using /ext as the root of the sync so you paths should start with /hosting/domain/storage....
To say you want this and anything under it, you use the ** operator.
So I think what you need is
/hosting/**
Note the leading / - you only want the hosting directory at the root to be excluded, not any hosting directory anywhere in the path (which is what you would get if you removed the leading /).