I understand that Jupiter is a very large planet, but why does it matter to the Rowan where in its orbit Callisto tower is, when the difference in spacial differences is minute compared to the overall distance required to 'port carriers to places such as Betelgeuse, Altair, Deneb VIII, Capella...?
My memory of the stories is that the ships still traverse the space between the start and the destination despite it being called "teleportation."
There are no other planets or stars in direct line between Callisto and the destination planets. To steal a phrase from Douglas Adams: space is big.
Jupiter is close enough to block them at the starting point. The Rowan can push a load to Jeff out at Deneb. She can push it to the side past the star and Jeff can pull it in the rest of the way.
Pushing past Jupiter means you have to go way off to the side - a straight line in those directions would put the load so far away from Deneb that Jeff couldn't grab it.