Valve depression length
The reason why piston valve ports are distorted (that's bumps to you and me, mate) is very simple. The distance of valve depression is directly related to how closely one squeezes together the three port holes in each valve.
Reduce the length of valve depression and we get bigger bumps in the ports where they overlap. Increase the length of valve depression and we get a smaller overlap (but still bumps) in the ports.
The answer then would appear obvious. Increase the valve length of depression until there is no overlap.
Well, er, actually no: if we did make the valve depression long enough to ensure clear ports, then by the time we'd have got the valves up and down a few times to play the Rheinmaiden's motif that evening, all the email database girls would have drowned, and Sir Georg's towel would have been realigned around my neck.
Pre-Wedgwood then, the answer has always been to compromise.
Vincent Bach designed an acceptable length of valve depression with an acceptable valve port distortion.
Mr Benge designed a slightly longer length of valve depression with lesser distortion in the ports.
Reynold Schilke, whose engineering is superb, went further by offsetting the valve casing ports.
Wedgwood, as usual, went further still and completed the process by
i) offsetting the valve casings,
ii) offsetting (non-axially boring) the valves themselves,
iii) increasing the valve diameter to "oversquare".
Phew!
This equation resulted in a shorter distance of valve length depression and no impedance (that's still bumps, mate) to the airflow through the instrument, giving a continuous uninterrupted bore of 12mm.