Sorry gents, don't mean to be a lazy poster but with March Break starting and coaching hockey I'm swamped. I was able to put this together in about 10 minutes so sorry for the crude line weights but I hope it will illustrate what I'm trying to do. The Styrofoam Form is 2 7/16" thick at the vertical edge. a 7/16" sheathing with 2" rigid on the wall system will make it about even at the outside face of the Styrofoam. I'm not using a standard stud wall, but didn't have time to show the structural panel wall for this detail. I am going to be using the 7.5" Greenstone Structural Solutions panels. https://www.gsbp.ca/.
I like the Pony wall idea and hadn't thought of that. I will give it a try later tonight to see if I can make it do what I need. I have also tried to activate my signature but just in case it doesn't come through I am using the CA X11 Beta right now, just changed over from X10 a couple weeks back.
Slab detail.pdf