Well, squadron transit would require both ships to have jump drives, but standard transit should have worked as your tug does indeed have a large enough jump drive for itself, and the tug itself is larger than the towed vessel. You could try a slightly micro-managey work around, tow the terra former to the jump point, then instruct the terra former to standard transit by itself, which it should do as the tug will be aT the jump point, then jump the tug and tow the former to the planet. You could try permenantly stationing a ship with a large jump drive at the jump point and using jump driveless tugs, you would however need another drive ship on the otherside or else it would be a oneway trip.