Answer:
Symbolic proportion is the tendency to create an image with apparent disproportion in comparison with the rest of the elements on the canvas.
Explanation:
In the piece your question is using as an example, if you look carefully, you can see that Mary and Christ are featured in disproportion to attest their importance on this piece of art. They're the bigger ones in the canvas and put in the center. That's the main use of the symbolic proportion. The objects and people portrayed doesn't need to follow the mathematical laws, because they're represented there to show their meaning.
