Since we are looking at the cylinder head while it is upside down, when I refer to something as being 'above' something else, it is actually 'below' the other thing while we are looking at it in these images.

The area 'above' the valve seats is known as the "bowl". Where the bowl turns and goes into the "runner" of the passage on its way to the port on the side of the head is known as the "transition". The transistion is the bend in the opening between the bowl and the runner. The bend has an outside radius and an inside radius. The inside radius is usually referred to as the "short side radius"....it is the short side of the bend.

The short side radius affects flow of the air and fuel mix on the intake side; and it affects the flow of the exhaust gases on the exhaust side.

Where the bend occurs, there is often a bit of an edge. Think of bending a drinking straw: the kink restricts flow of the fluid you are trying to drink. The 'kink' is almost like an archway under a bridge.

On the exhaust port/runner/bowl, that edge is pretty sharp, especially right in the middle. I will just round off the sharpness of the edge at the middle of the bend on the short side radius to smooth the flow a bit. And as shown, there is a shelf on the sides of the bend, corresponding to the legs of an arch. These shelves are a result of the machining process when the seat inserts are installed. Thses shelves restrict flow as well. I will grind down the shelves to open up the bend a bit to help flow....in other words, I will widen the arch, but not make it "taller".