Here are the long ago promised pictures of adding the elastic to the sash of the Fledge/studio TANTRUM pattern, Feliz. This particuliar Feliz dress is made from European fabrics from banberry PLACE, a bizzkids plaid that matches perfectly with a hilco corduroy and a new green solid cord, also from bizzkids.
I used some black interfacing to help secure the seam, cut a 3.5 inch piece of, oh heck – I think it's 7/8" elastic – 1 inch is closer to the same width of the sash and I prefer it but was temporarily out, and stitched it to both the end of the sash and to the dress seam. I took a shot of the 
back elastic too, I use 5/8" elastic and only did 2 rows. This is a size 128 and you can see how tightly it's pulled. Pulling it so tight make for a better fit, in my opinion.
I can’t see the Feliz pics! And I really need to see the pics! Am making a Feliz and my pattern is wrong.