Looking up fares on the Stagecoach website for St Andrews to Edinburgh on the X58/X59.
It says a single is £14 but a day return is only £8.10?
East Scotland Dayrider is £12.20.
Why does a single that costs more than a dayrider even exist?
£14 does seem to be a somewhat standard single for these longer routes - it's also given as the fare for:
Aberdeen - Dundee
Dundee - Edinburgh
St Andrews - Glasgow
Edinburgh Airport - Auchtermuchty/St Andrews
Kirkcaldy - Dundee
Stirling - Dunfermline (this doesn't even leave the West Fife region, whose day ticket is £9)
Cupar - Dunfermline (a journey which could be done on a £3.70 evening rider after 6pm...)
Bizarrely there is even a case where split ticketing now exists on their buses. The fare between Dunfermline and Alloa is £7.80, between Alloa and Stirling it's £5.60 - so that's a total of £13.40 vs a single fare of £14. It's even worse for journeys between Dunfermline and the small town of Tullibody between Alloa and Stirling - £12.90 vs £11.60 (£7.80+£2.80) or more than £1 difference!
This is all somewhat academic as I suspect very few single fares are sold, though it may catch a few tourists travelling between the Airport and St Andrews. But it does seem quite perverse given the reimbursement system.
For instance, a journey such as Cupar to Stirling as a day trip is eminently reasonable. Indeed, not only do the X24 and X22 connect well at Dunfermline, but the day ticket (£12.20) undercuts the rail fare even with a railcard. I am sure people will have genuinely done this journey (it's not a weird edge case like Aberdeen to Edinburgh for hours and hours on local buses which I have admittedly done but wouldn't be a typical travel pattern).
If someone uses a concessionary pass to travel on this journey, then the system assumes that they would have paid £56 - far more than what anyone would consider reasonable for that journey and obviously nearly five times what said passholder would have paid if they were a 22-59 year old adult. Looking at how the reimbursement works it would appear Stagecoach would be reimbursed somewhere between £26.82 and £40.54. This thread probably isn't the right place to delve too much into the weeds of the system, but it really is a bit of a mess...