[Phantom]

I believe you are referring to the area around FL#30

FL#30 is associated with a Black Top and "safe passage is to the northern side of it

The Red & Black Tops that you see close by mark a hazard between them. Counter intuitive but (as stated) the safe passage is between the shoreline and Red Top

Many people get confused and think the two black tops in the same area are associated with each other -

Just goes to show the Cardinal system is not perfect. There are a select few of these types of situations that you just have to memorize. Another is over by Varney island.