I don't think 9 would be too many. I didn't do the original chop, but it appears to my eye, it was a straight chop, and not a V chop. I think a V helps to reduce the bulging outwards. (I need to do more research.) Perhaps hollowing out the V, and/or multiple V cuts all around the trunk.
Boon showed me an article in a Japanese language magazine where it appears to have about 20 new branches grow from the chop! Maybe even more. But it appears the aftercare is important. It looks like the trunk was bound, and the new branches bound so that any swelling was directed inward as they grew. They were allowed to grow two or three feet tall, getting as big around as a pencil, then cut back to 1 or 2 inches, and the process was started over again.