I am not sure this is exactly correct but a longarm is generally considered 18"+ and the midarm is anything between 10" to 18".
I also have a Juki TL98Q which has a 9" throat area and have no problems quilting a king size on it. It takes practice but can be done by bundling...it's really not that hard. I have a frame for it but actually prefer using it without it. The frame sits in a closet.