SBM head velocities and there application?

So eg. Say Trick Flows 300 cfm with a 190 cc port.

Is trick flows port length 4.95" ?
For now I'm gonna go with that.

Average csa = port cc / 81.12
190 / 81.12 = 2.34" ave csa.

Port fps = cfm x 2.4 / ave csa
308 fps = 300 x 2.4 / 2.34"

To get 260 fps the ave csa and port cc would need to be 2.77" and 225 cc a pretty large port especially for 300 cfm.