A flying saucer isn't really a suitable wheel.They're very gimmicky unfortunately as they do claim they're more natural but in reality they are not capable of allowing a natural running position
No matter what species or size,the wheel will always cause side arching due to the shape and structure of the wheel.
However,you could put money towards investing in a much better quality wheel such as a 9 inch Silent Runner which would be perfect for any dwarf species!They cost a bit more than some of the more readily available wheels,but they are of superior quality and are much safer.