unshrouding the valve will "somtimes" increase air flow, it depends on the head,
Some heads dont even flow much air on the wall or shrouded side
I remeber spending hours reworking the chambers on a set of 492s, i made a speisel tool for cutting the side of the chamber as well as having it angle out so as the valve opened it becance more de-shorded, in the end i only picked up a few more feet per minute.
In a racing enviroment where every little bit adds up to an edge, it mite make more sence.
Its easyer to pick up more air flow by shaping the bowl aera so
air tends to flow more to the centre.
I look at it like how can i grind this so works like a helix
Just look at the chamber of a vortec head to see how smaller valves flow more air.