I put three quarter inch sashing throughout, and on the edge. My tris were the regular size, because I used the ruler, and didn't think early enough that I would do the larger sashings, so that I could cut larger. I compensated with larger in between tris. I cut them a quarter inch larger on both long sides. It just meant that when sewn on, they didn't go down to a point.
When it came to adding the scollops, I also cut them deeper, so there is a seam about 1 1/4in deep (when sewn on) between each scollop. i.e. I cut them 1 3/4in deep, with the curve added on after that. Hope the pics help.