I have 2 IX 3 layer UQs both built the same as the OP but with head and foot end draft tubes. I put one one top of the other, bottom UQ hung looser than the top UQ.
Works great for the back yard. Got down to 28f last night with a feels like 22f I was warm and toasty.
Too bulky for the trail. You can make a climashield or primaloft UQ and velcro it on to the top of the 3 layer IX. Or sew it in with one line of stitching and seam rip it off when the weather breaks.
How low temp are you trying to go?