According to the history of the word 'model', the phrase 'big model' is an oxymoron. See WhatIsaModel
But not in Architecture, when big models have a large WowFactor!
All right, you've forced the relativity argument. Nothing is 'big', except compared to something else. A 'big' Architectural model may be 'big' compared to the guy who's viewing it, and may be 'big' compared to some smaller models, but must still be 'small' compared to the thing it models, or else it's the thing itself, not the model. Sorry, it's by definition.