@ Fore
I do two configurations with tiles, single tree and five trees. The size of the tile is 4" regardless of the intended size of he tree. The tile is only there to start the base in the right direction and without regular rootwork a few strong roots will become dominant. Think of it like the spokes of a wheel. the farther away from the base the wider the spaces. Everyone has their own appreciation of what a base should look like and this technique is at one end of the spectrum and basically doing nothing is at the other end.
@Painter
As far as zone, I don't know, I'm guessing Z7. Oregon, foothills of the Cascades and zone changes can occur in a few feet depending on elevation. Climate zones are a crude guide for growing trees. Gives you an idea of minimum winter temps but there are so many other variables for good growing that are just as important. I do rootwork in the fall but the trees are greenhouse protected with high humidity. Funny story, I worked this tree 11-8-12 and looked at the potting tag afterward and it was potted 11-8-10 with surface rootwork nov. last year