I'm quilting an embroidered quilt right now. The images are centered on larger blocks with open area around them. It's a really cute quilt that a customer made with Halloween houses around the outside and a pieced center area. I'm doing a panto on the pieced area and custom quilting the outside. Due to budget constraints I am just stippling around the houses, but if I had unlimited budget I would probably try to quilt clouds in the sky...grass on the lawn, etc. I am doing a single echo around the houses, and leaving the bulk of the embroidered area unquilted. These designs were hand embroidered. There is enough quilting to meet the restrictions of the batting, and the designs pop somewhat like trapunto. If you are working with machine embroidered designs which are much stiffer than hand embroidered I would try to quilt closer together. I wouldn't ever quilt over the embroidery, just look for open areas inside the pattern that could use a little quilting. Hope your project is fun to do, I love the quilting part.
Susan