Thanks Splintergroup!
I did set the box to the side of the blade, but somehow misjudged so the cuts were too shallow. Guess I was being overly cautious on not cutting into the box. The second box went much better so hopefully I'm getting better at the setup. I did follow your comment on my prior project of waiting to cut the top free until I had all the splines done. Given the sides were much narrower, this allowed for all the corners to be "set" before separating the parts. Appreciate your help!