Does anyone here understand the logic by which TOCs decide the addon cost
of Day Travelcards over Day Returns to London Terminals?

Looking at a random selection of towns and cities around London most seem
to be in the range £2.50-£4.50 (before railcard discounts). All except
FCC, that is. The Huntingdon addon is £5 while Cambridge seems to have to
highest of all at £6.

Above £4.50 and the point of Travelcards is destroyed for most users who
only make 2 tube journeys and have railcards and Oyster.

--
Colin Rosenstiel