That's true, and is a good argument for looking for some way to eventually extend contactless to the entire UK (Or at least, to GB). However, I imagine that by moving the boundary further away from London, it's possible that Project Oval will reduce the total numbers of people getting confused, purely because the boundary will now be located in an area where fewer people make rail journeys.
(On the other hand, if the boundary is now in an area where there are more unstaffed stations, then it could increase the proportion of people deliberately chancing it for local journeys that don't go into London
)