Hi,
So, I've had a read through Apple's documentation a few times
The system matches URLs using string-based root matching. A URL matches an allow list, deny list, or permitted list pattern if the exact characters of the pattern appear as the root of the URL. For example, if the system doesn’t allow test.com/a, it also blocks test.com, test.com/b, and test.com/c/d/e. Matching also discards subdomain prefixes, so if the system doesn’t allow test.com/a, it also blocks m.test.com.
So, if this works as expected, you should be able to add just studyisland.com and you should be good
Let us know how you get on.