Hi,
You’ve touched on the subject which is occupying my time at present, namely understanding PAYG cap extension fares on contactless. I’ve been waiting for a response from GWR which has just come in and I’m about to write up the story so far. I am also intending to involve London Travelwatch, because the process is far from transparent. I believe it should be possible to work out in advance how much you will be charged for a sequence of journeys, which currently isn’t doable.
One issue to bear in mind is that a PAYG extension fare will cover both Slade Green to Abbey Wood and Southall to Maidenhead, whereas a paper BZ4 to Maidenhead ticket will only cover that end. It’s possible that I may be able to work out what the extension fare is once I know what the new NR fares will be, but the insistance of the DfT that new fares will not be made public until March 3rd is hampering even basic research.
Watch this space!