i struggle with getting the measurements right, so I thought these from "experts" will be better to show you how they would do it. Funny....now I have to go watch them. I know I can pick up some tips.
https://www.youtube.com/watch?v=Q6YUigIrTJk
https://www.youtube.com/watch?v=1790TY4ddbI
https://www.youtube.com/watch?v=fpRQFWxWKPs