I have a small 4 x4 Christmas tree layout I'm working on. I ordered some supplies from my favorite online store. One of the items was ballast. I believe most people use different size ballast and maybe even colors... What sizes do you use for Ho? I bought fine and it seems too small. Should I buy a medium now with a minor variation in color? The ballast will not be exposed as much as most layouts... I'm covering it with woodland scenics snow.