Great question. To be honest calculating actual model size is much more trickier but for Level 2 folks it should be enough for them to understand .
To answer your question - Model Size really doesn't depend directly on the number of modules that are created in the model. It is the line items that make up the modules and it is the cells that are counted within line items, ultimately it is the number of cells only that derive the model size based on the formatting of those cells. Add to it the list items you get to arrive at approx model size if not accurate