I realized that in my quarter block diagram, that didn't show the full triangle in the center of the block. I pulled out my handy sheet of graph paper and have it drawn to size, but it's been awhile since I've fired up Electric Quilt so I'll do that and get a PDF of their cutting instructions. Be back in a couple with better info for you
Oh gosh! It looks like Electric quilt sets it up as 3 across and so has a bit different parts. That makes the corner squares 3" unfinished...
So talk to me and we'll figure out which variation to go forward on!!