How did you find the regular path? I've been checked RTT for a while, not a lot seems to be coming out of Long Marston or Honeyborne North junction.
I was shown it at the time, wish I'd paid more attention to the head code as I can't find it myself now.
Be aware, anything going to Cardiff from Long Marston will most likely be a 153. The 230s will be heading north. Certainly wouldn't expect to see a TfW move this month at least.