Originally Posted by ghostrider

There is no real trick to designing on-point quilts. It's easier for most people to see/plan things straight on than tilted, so design it as a square setting and then turn it 45° and add/subtract along the edges to square it up again. If you can draw it straight, you can make it on-point.

I can't picture the layout you want, but I think graph paper would be the simplest way to see if the 10" and 12" combo fits to your liking.