I don't know if luck plays into getting eles to spawn. Your mining does determine what you get. If you mine up Valorite, you will get a valorite ele. You randomly can get 5 eles to spawn in one spot or you can get 1. I have yet to kill a ele and not get a arty, so from my experience each ele drops a runic. I used to be they dropped runic tinker kits aswell as hammers.