BBC South would probably argue that commuters in Oxford's tx area might be affected by the Southern problems because of rail links to Reading and Bletchley. It's possibly a bit tenuous, but Reading and MK stories are regularly covered by the sub opt because they're of interest and not outrageously un-local.
Historically Oxford has always taken BBC South opt out regional programmes, though it's completely possible not to and stay with the network. The regional series Sea City was shown pan regionally despite places like Banbury being about as far away from the sea as it's possible to get.
I can only recall one occasion where Oxford didn't take a BBC South programme, it was an Inside Out I think, which for reasons now I can't remember, had aired in the Oxford region but didn't air on Rowridge or Hannington. The next week, Oxford stayed with the network, opting only for the ident explaining that the London edition would be shown, while the South caught up. The South then opted on its own for an additional week to get the last of the series out.
Two minutes regions...