You need a potato that produces multiple layers. Yukon gold only produces a single layer so adding soil to it does do anything. I've heard most fingerling potatoes produce multiple layers. You could also try planting the potatoes and layers all at once and placing you seed potatoes along the edge( eyes pointing to the edge) with straw as the border between soils and wire. The potatoes supposedly will grow outward instead of up and thru the straw. You end up with potatoes growing in multiple levels. I've read claims of being able to grow 90 pounds in a 2x2 foot area. I'm actually going to try both ways this year with fingerlings as my fill as they grow plant and Yukon gold as my fill al at once tower.