Couple of basic things I noticed. Iwagumi is generally odd number of stones. It's suppose to be the randomness of nature, even numbers are usually more structured and man-made.
Also you don't want you biggest stone all the way to the side. Generally the biggest stone is the focal and you want that more in the middle off-center and the smaller stones to support it (not physically touching it, just to work with it).
You could do what you want, but by definition that is more what an iwagumi about.