Velocity or Suction?

OK, so I have been around for a few decades in this and always accepted the idea that flow velocity is important in cylinder head ports. But I got to wondering if flow velocity is the really important thing or is it suction through the ports that is important. I don't pretend to know the answers here... just looking for knowledge.

Port flow is not constant unless you are high enough RPM to get near to a resonant situation. Flow starts-stops-starts-stops..... So if you are at lower RPM's and the port flow has to be started when the intake opens, does a smaller port allow the cylinder suction to work better to start drawing the A/F mixture? Is it like drawing a drink through a straw....too large a straw makes it hard? (Forget milkshakes.... that is viscous flow!)

Or, is it really flow velocity that counts? This would seem to only be effective in the closing half of the cylinder filling cycle, to help jam more mixture in after it gets flowing. A low velocity, large air column would have less kinetic energy in it (1/2 mv^2)than a smaller, high velocity air column..... (but you have to put more energy into it to get to that state).

And, do we talk about port velocity because that can be measured on a bench in a controlled, repeatable fashion, and that somehow correlates to better performance aspects, but is not really what is happening?

Like I said, just looking for knowledge....tnx.