Vision NA? (Scuttle vision not accurate)

This is what I see: https://gyazo.com/94735490c8e54065549e746bee0e46a6 this is what's happening: https://gyazo.com/eadf0f3ced4c1f1e2788dfff62940fe5 These pictures are at the same moment of time. It would appear that I should've seen Hec coming, but I didn''t. If anything, the vision area that the crab appears to give is not accurate, but what would be the point of it if you can just walk around it?