I shave a bit and put 9 frames in and it works great.

But I also have a few follower boards around here and they make up the difference pretty well. I "inherited" a bunch of "Honey master" frames that I cut down to mediums and also use for followers. They would work better if they were 13" instead of 13 3/4". But then I wouldn't be able to put 9 frames in them...
I also find that one PermaComb (which have no spacers) with eight regular frames is just right to fill them out to 9 frames