Are there places that a Ride-Height Mod (RHM) unit cannot go that an unmodified one can then? Or are you simply saying that it is difficult to work out which services these particular units are on for anyone wanting to see/ride-on one of them?
RHM 165s ok anywhere except Henley Branch
RHM 166s ok anywhere except Newbury - Bedwyn (although 221 has been to Bedwyn)
Neither can run to Banbury.
RHMs coupling to Non-RHMs should be avoided where possible - it can be done but it’s not guaranteed to couple. If needs be we’ll do it at Reading or on depot but won’t plan to do it out in the wild.
The upshot is Reading Depot and LTV Control have to consult closely to make sure RHMs are on suitable diagrams.
North Downs and Basingstokes are more likely to see RHMs, because those diagrams don’t normally see Oxford (and thus risk of ending up on Banburys).