Position of reversed circles after b and p (Anniversary)

When a reversed circle follows ish, chay, j, f, or v, and and m or n follows the reversed circle, the m or n is written above the circle; but when a reversed circle follows p or b and precedes m or n, the m or n is written below the circle.  Writing the m or n above the reversed circle in all cases seems more logical and makes it easier to keep the m or n straight.
Can anyone explain why the manual calls for writing the m or n below a reversed circle that follows p, b, or left s?

(by bruceeford for everyone)