I am the proud new owner of a long arm machine. When I bought the machine, they sold me needles, size 18. First 2 quilts turned out fine, using Warm & Natural batting, but the one I am working on now has a red backing & I'm using Hobbs batting & it is coming through on the back! Not heavily, but very noticeable on the red backing. My question is, why do I have to use such a big needle?