Selig Z Chairs Cushion Thickness?  

Hi all. l Can anyone tell me what thickness foam should be used for the cushions on a Selig Z chair? I'm making new cushions and replacing the Fagas straps. I've seen many photos with different sizes, and would like to keep them as original as possible. Unfortunately the original cushions are long gone. I've seen a photo on the Evans Furniture Co. website. The seat looks thicker than the back.
Would a 3" seat and 2" back cushion be appropriate or 4" seat and 3" back.

Any help would be great!

Thank you.