Thank you Professor Pincushion for getting back to me so quickly. I was wondering whether there was a way where the chiffon could be free below the zip (other than way I mentioned) as the dress is a circle skirt and I wanted them to flair out separately, but I think I agree with you that this is probably not going to be possible due to the instability of the fabric and I need to sew them in together below the zip as well as you suggest.

Not a fan of chiffon I have to say!!!

Once again, thank you so much for your help.