Its true, and will effect these 'countryside' or the less connected schools the hardest.
Those in commuter belt towns, larger towns/cities that are to an extent, 'well off', with rail links to London or close to the main motorways will do ok I think. I live there, so its my prime example, but towns like Guildford, or others like StAlbans, will remain popular, due to their positioning.
Especially, as the market for independent schools contracts, and is less saturated, due to the closures of remote or smaller school, those that remain will prob be able to sustain and do well.
The sad thing is, it's a spiral, once parents see a school not seemingly 'prosper', I.e. small number, slightly tatty round the edges, not perceived to be doing well, no investment, etc. Then they steer clear in favour of the financially stronger institutions.