I know free space half wave dipole length in feet is 492/f mhz.
I also know 468/f mhz is for "antenna cross section...stray
capacitance...called end effect because the ends of the antenna are
made farther apart electrically than they are physically..." as laid
out in the "Practical Antenna Handbook 3rd edition p.138".

This is suspiciously close to the 95% velocity propagation of parallel
line.
My question is, for a given coax with 66% velocity propagation, is the
formula 66% of 492 (325/f) or
66% of 468 (309/f)?

Thanks in advance