Your blocks are beautiful! I've never gotten that many points to come together so perfectly! I'm impressed.
I'm with the others on the scant ¼". I just try to get a couple of threads closer to the edge and it seems to work pretty well. I'm surprised the one that you pressed with the seams open didn't come out a little larger though. I've heard that pressing to one side is the reason we have to go to a scant to make the blocks come out the right size.
Hope you get it worked out Flying_V because it's sure going to be beautiful when you're done!!