The speeds quoted are, of course, averages, and not an accurate picture of port conditions even in the (theoretical) range of maximum piston-derived vacuum (somewhere near both the ICL and the highest piston velocity - typically in the mid-70s depending on the rod ratio).
With a strong exhaust pulse, the vacuum across the chamber during overlap is stronger than piston vacuum. The static conditions in the chamber between high and low compression (small vs. large chamber volume) and high and low rod ratio are fairly different. In relative terms, cross-chamber flow is "lazy" with a really long rod (like n=2) and low compression. This effect is almost harmless if the port is too small (vs. displacement), and very annoying if the port is too big. The reverse condition (short rod, high compression) is significantly less affected by this factor.