The circle is often associated with an angels crown. Putting it above the A and using the circle as part of the A shows the angel aspect to the companies logo. Also having it above gives that guardian feel.
Oxus Treasure; finger-ring; Achaemenid; 5thC BC-4thC BC; Takht-i Kuwad. Gold finger-ring with stirrup-shaped hoop, thicker at the back than at the shoulders, expanding towards a flat oval bezel with a slightly projecting edge; the bezel is engraved with a winged bull with crowned and bearded human head; an Aramaic inscription in the field above; a sign resembling a caduceus placed horizontally is before the bull's breast.