I make it about 15.5 metres in the bus lane, using your GSV link. At one time the Traffic Penalty Tribunal applied a 20 metre "rule" as the basis for a
de minimis (trivial offence), appeal, but I'm not sure if this is still done. However
de minimis is very much subjective, so a win at the TPT is not guaranteed. Having said that, your first move has to be to submit representations on that very basis quoting the GSV distance. Don't expect them to roll over, as money is now their sole interest in things like this. Certainly advice here for
all PCNs is to first submit representations, as so many councils
****-up their response. Why make it easy for them by paying up straightaway ?