Now, think of all those beautifully machined sharp edges surrounding the dish and valve reliefs.
They're like little waterfalls, in which the overlap leaving the valve seats near TDC flows.
Yes, the flow trips over them, and reduces the effective area of your overlap triangle.
If you cam is too small, you're losing power that could be recovered by adding a 1/8" radius to all those edges.

A finished piston may have sharp edges to control flow, but not as shown.