I went ahead and put a 6ml square soy bottle in one of my Mini 2.1's to see how it goes. Should cut my refills in half. The caps on my soy bottles are hard plastic, have a molded in inner sealing ring that goes into the bottle just a little. But it was fast easy work to get it bored just right with a Dremel and a tapered burr. It was a tight fit getting the battery back in, and I have to push the bottle in some to slide the door back on. So there definitely won't be any rattles .