Self-Draining Terracotta Soap Dish

I have tried cleaning the wall wedding the non-slippery suction cups, but the promising bar holders just won’t stay stuck. They keep falling down and a piece of one of the bars chipped off. I’m not sure exactly why it won’t hold the way that maybe it’s the way it’s designed. At best one will slip a little bit and then all the bars fall out. At present, I have just sitting on the edge of the tub, but unfortunately it’s in the line of water from the shower so probably the bars will dissolve a little faster.