According to 'Dowding of Fighter Command', it seems Duxford nearly ended up as part of 11 Group. Vincent Orange suggests that if it had, then Bader would have got more of the battle he was after and Leigh Mallory would have been denied his support.
The other solution would have been, to send Bader and his Squadron to join 11 Group. It's a mystery why it never did, 'Sailor' Malan, came from 11 Group and joined the Bader wing for a short time, before going back to 11 Group, yet Leigh-Mallory ensured that Bader stayed put.