Contactless is only valid on the lines shown on
TfL's Rail & Tube map. This doesn't include the SWR route to/from Reading via Wokingham at the moment - on that route the furthest west you can go is the last station in Zone 6, Feltham.
Therefore you couldn't travel Maidenhead - Reading - (Wokingham -) Richmond on contactless.
You could do Maidenhead - Reading - Paddington - Earls Court - Richmond or similar if you wanted, as there is nothing stopping you from doubling back (e.g. via Reading) within the contactless area of validity, other than the
maximum journey times. But it would be fairly pointless as going directly towards London would usually be quicker.
Note that the £6.20 off-peak PAYG fare is the 'default' fare which is charged if you don't meet the conditions for any other route. A higher off-peak fare of £10.80 is charged if you interchange between Underground and National Rail services at Waterloo, Blackfriars, Cannon Street, Charing Cross, London Bridge, Victoria, Southwark/Waterloo East, Battersea Power Station/Queenstown Road or Vauxhall.
This is because you would incur the so-called 'mixed mode tax' since the SWR/Southern routes out of London are charged at the "National Rail" fare scale as compared to the TfL-scale fares that apply on the Underground and certain National Rail routes such as the GWML. Changing at Paddington is therefore fine - that will be charged at the default fare since you are on TfL-scale routes throughout. For more information on the fare scales
see here.
