Porting a slant six head

These pictures were so clear I thought I could use them for another question.

Why are these cast this way in that they have this raised area? I am going to assume that I should leave this raised area alone? Dont try and remove it but instead just sorta smooth mine out.

If I did know any better I would try my best to just flatten this area. But at some point there is going to have to be a bump in the head for the valve guide to pop thru and so maybe this runner is sort of a transition so there is no sharp change of angle within the port?