What is the correct way to put the lettering on the WWII British aircraft? I've seen pictures with the lettering on both sides put on in different ways. With three letters does two letters always go between the Roundels and cockpit on both sides or does the unit designation, example MD go on the same side of the roundel, thus having the roundel further forward on one side than the other. Or did different units do it how ever they chose?

Example:
Left side
Cockpit MX Roundel A Tail
Right side
Cockpit AX Roundel M Tail

Or
Left side
Cockpit MX Roundel A Tail
Right side
Cockpit A Roundel XM Tail