ILM made a scale sheet for ANH. I have a copy of it somewhere.

Even still though, stuff like that was a loose reference. They didn't put as much thought into it as anyone here is. Whatever looks good by eye, when theres 100 other elements flying around and the shot goes by in 4 seconds, is how they judged how to composite the things; if its off, who cares, as long as it looks okay when there's 100 other spaceships flying by and the shot ends before you can even figure out if its off or not. Like the shrinking ROTJ blockade runner. Scrutinizing it shot by shot to determine precise scale is pretty fruitless because it will never match perfectly. There is no precise scale in the films, only a general one that perpetually changes, so whatever you attempt to "standardize" in one way will be wrong in another way. I say just accept that its a movie and move on.