QuiltE

Picking up on BearIsGray's suggestions

... some of us audition the fabrics, and the widths of the window frames
by actually sewing a block or two, to see if we like it ... or not!
And re-do it a time or two until we get what we like and want!

I usually do those with a longer stitch length,
so that it's easy enough to remove if I want to make changes.
Just be sure to remember to re-stitch them, once you get what you want.

Again, no formula ... it's all about what you like ... You Do You!