A.I. ships dodging my ships during their retreat after AI loses naval battle

So I have searched the web for an answer to this thing that I cant quite figure out. When an enemy fleet is beaten, are they supposed to just be unable to be caught, no matter what? I've tried catching up to them, getting to their destination before them, actually having ships stationed all around a battle in order to "catch" the fleeing defeated fleet, but no matter what I do, the enemy ships just glide through without any engagement.

Solution 1:

Armies and fleets that are in shatter retreat can't be intercepted. They arrive at their destination and only then it becomes possible to engage them. Unlike armies, fleets retreat to port, and you can't attack them there. You can occupy the port province and force the fleet into the sea.

You can recognize shattered enemies by a small white flag icon.