relief is old school, you need to flow air over the top of the valve to utilize the entire diameter of the valve and max flow. The combustion chamber in the head is more inportant
I agree, the relief (as shown) assumes that air will follow the floor, and drop down into the bore. IMHO the only "working" part of it is where it exposes the valve seat to the gasket surface immediately on valve opening. From there, the relief depth should decay as it approaches the bore (shallow angle to reach the seat depth and be flush at the bore edge).
I suspect that a generous radius at the bore edge (like 3/16") would improve VE and reduce pumping loss, but it does add a bit to chamber volume, and must stop at least 1/16" (more = better) above the highest point of ring travel @ TDC or the ring will overheat and lose tension.
The area above (and behind) the valve is more important, since the flows will tend to expand upward and away from the valve.
To conserve compression, the relief behind the valve can be partially filled following the general idea used in the Harley-Davidson KR diagrams.
Important: the width of the relief (deck and head) where the relief enters the bore should not be increased, this is a major part of the original Ricardo turbulent quench head. Chamber turbulence is not reduced by porting but is dependent on quench, if possible reduce the piston to head clearance to .040". Milling the head will not do this unless the piston has positive deck, you have to deck the block (or increase the rod length, stroke length, or compression distance).
