Not sure that's true anymore, at least for some ship models that were added subsequently. One thing I've noticed, for example, is that the original ships, such as the Sidewinder, Cobra and Python all would have extended ramps with steps while landed. Later ships increasingly had no such detail included. Also some ship internals, such as fighter bays, did not exist when those original designs were created - there's no reason to assume that they have been designed to 'fit in' as well.Lord Braben Himself, from the very early days of the game, paraphrased: "One thing we built into the structure of the game is ship interiors, and being able to walk around them and on planets and in stations on foot. We've designed all the ships with interiors in mind, how the cargo is loaded and unloaded, "
I'm sure an effort to design the ships to allow for interiors was originally the case, but I suspect that this wasn't consistently maintained. Chances are they'd probably have to go back to the drawing board at this stage.