Coaxial crossover conundrum

GM, please can you define the parameters and phrases you use in posts #18 and 20, in common language or a picture

Vc frequency
TL modes
driver's Fs
VC's diameter
theoretical BW of a point source

How do you "calculate the mean of the 1st xo point and VC" and why should we do that?
If VC's diameter means voice coil's diameter, what on earth has it to do with acoustic performance?