Hi again
There's an interesting passage about RAF fighters in Europe at the War's end in Michael Bowyer's Fighting Colours:
"...Another feature was the introduction of Type C roundels above the wings on both 2nd TAF and ADGB fighters. About March, many squadrons added a thin yellow surround to these, but no specific order seems to have been given to do this."
I found the following pics of Tempests with the yellow surround, but the variation in roundel sizes is also interesting:


I hope this helps.
Rowan