Whose profiles are visible to me?

At one point I recall seeing that I have access to the profiles of people out to fourth cousins. But it's not clear to me where the cut-off points are in the case of peripheral connections to my family tree. For example, one person in question is the ex-husband of my first cousin once removed. He is visible to me, as of course are his children, who are my first cousins twice removed. On the other hand, I cannot see the profiles of his siblings and parents, though I can see their names on his own profile.

On the other hand, the great grandmother of my aunt by marriage has a profile I can fully access, including editing. I can't really figure out what the rules are..