Yea, but it is easy to visualize the air flowing into the combustion chamber having to bounce off that close vertical combustion chamber wall and causing a restriction. At the same pressure more air will flow through a 2 inch hole than through a 1/2 inch hole.
And I have seen flow improvements on my flow bench when the valve shrouding was relieved.
Two more things, 1) when working to improve port flow, there is almost no place easier to work and with less risk than the combustion chamber wall next to the valve, just leave room for the head gasket seal.
2) one of the critical set up characteristics when doing flow bench work is duplicating the cylinder diameter of the block that the head being tested will run on. Blow the cylinder diameter out larger and flow values go up. That is evidence that valve shrouding has an effect.
