I think any of those maps don't pass muster. The fatal flaw is shown in the monthly stats for each unit, take the Boreham unit, the greater proportion of its flights are to the south and west, Basildon, Southend, North Kent etc. The centre of the circle might be at Boreham, but operationally the aircraft is mainly flying off centre and will require fuel at Boreham before redeploying in the Suffolk and Norfolk direction, rarely will it be Sat fat dumb and happy at Boreham waiting for Norfolk to call. I'd imagine this is the case in many other circles.