ILM built the hero 6' model, and the 2' model. Both could be saucer separated. Both evilnate
are correct. The long shot wide-angle banking scenes of the two separate sections were easier to set up with the smaller model. To stage it with the 6' model at the same scaled distance, would require enough stage room for the camera to make that banking turn. And setting up the 6' foot model was likely more expensive on the budget. Most of the separations seen are recyclings from 'Encounter at Farpoint'.
What about movies like ROTJ? All the distance shots during the battle of Endor were done with small models or was ILM's shooting stage that big?
Again, it's budget. You're asking for the comparison of a major motion picture with a single television episode's money to play with. ILM had more model makers, more effects artists, etc., to work with. I've not seen photos of the model redwood forest in years, but I think the trees were as tall as a man. Star Wars miniature sets were often fairly large. We can't always be sure if we're looking at just a miniature or one enhanced by a matte painting.