I don't know about anybody else, but I smooth the edges of the dummy first before I apply fondant on them. I also tend to roll out the fondant a little thicker for dummies then regalur cakes. Hope that helps.
I don't suffer from insanity; I enjoy every minute of it.
I sand the edges down too. I am ok with covering cakes, but I cannot get my corners sharp like more profesh bakers, and dummies always make the fondant look so sharp, and the real cake tier never matches. This way, it looks more uniform.