The line for conjurations I believe you are thinking of, [MENTION=69684]WEContact[/MENTION], is:
QUOTE
Occupies No Squares: The conjuration occupies no squares. The conjuration does not need to be supported by a solid surface, so it can float in the air.
END QUOTE
However... the entry for Call Spirit Companion states:
Effect: You conjure your spirit companion in an unoccupied square in the burst. The spirit lasts until you fall unconscious or until you dismiss it as a minor action. The spirit occupies 1 square.
Therefore, in this case, the spirit must be supported by a solid surface. I have no problem with it being summoned in the air... but then it would immediately fall to the ground.
As such, Ursa Maximus should be moved to its own square.