Hi Colin,
The old extensions are still available. Rye House to Boundary Zone 6 is £6.50 single, £6.60 super off-peak day return, £7.70 off-peak day return and £11.20 anytime return.
The ticket machine cannot offer the PAYG fare because that is only available when using the PAYG system. Part of the reason for the discrepancy is the disparity between singles and returns on paper. As PAYG only operates as single fares it was necessary to make the single fare half the required return fare.