I did an un-planned set of trips on Wednesday, which quite by chance
emulated the Oyster capping conundrum discussed here recently.

viz: Several trips within Z12, all charged to £2.10 each until I hit the
off-peak cap of £7, and then later in the day a sole Z13 trip.

If I had bought that last trip in isolation it would have cost £3.20
because it was during the evening peak, but because the *cap* doesn't
have an evening peak period I was only charged 70p, via the higher Z13
cap of £7.70

This lack of triggering a Z123 peak cap, within the journey scenario
above, makes it moot whether the day's travel would be charged at the
Z13 peak cap (£10.60), or the sum of a Z12 offpeak Travelcard (£7.30) +
a peak Z23 single (£1.60) - which totals £1.70p less.

I hope that's completely put the conundrum to bed!
--
Roland Perry