Gordon Jennings in his book under the heading "Port Timing" gives a thorough analysis on how the two stroke engine porting systems work. He argues astutely that the flow of the port is a function of it's mean cross sectional area (the mean area of the port as the piston opens and closes the port during the cycle, not the total port area) and the amount of time the port is open in crank degrees.

He has developed a parameter he calls "time-area", an idea that was actually first introduced by Yamaha engineers. He then normalizes this time-area parameter (divides) by the swept volume of the piston in the cylinder (displacement). This simply means that for a bigger cylinder you need bigger ports! He has found that with this calculation you can then introduce engine speed into the calculation and tune the ports to work at what ever speed you desire to obtain peak torque.

So, although port volume may take a part in the performance of the two stroke motor, affecting things such as port scavenging because of the different velocities as you mentioned, it is probably of only secondary effect. The first order effect is the cross sectional area of the port and the duration of it's opening.

Do read Jennings section on Port Timing, for he does a much more thorough job of describing the concept than I.

diceco