what is the best way to figure cross sectional area. and at what points in the runner should you measure?

also anyone know a better way to get an Idea of potential velocity from a cylinder head. so far this is what I have been doing. when planing or relating a set of heads to an already assembled shortblock. I take the lift of the cam say it's .600 lift I add all the flow #'s from .200 to .600 I only use the last .500 worth of lift and then I pull an average from that. after I get the average I devide it by the cc of the runner to gat a number that represents how many cfm per cc of runner the head has. I don't know realy what to call it but in my notes I call it VR for velocity ratio. and I've had some dyno charts and engine combo's that seem to point that heads with the same cubes and vr's tend to make tq in close to the same rpm area's even if one has a bigger runner.

any other thoughts or input would be apreciated

sorry for my spelling and gramer.