Maybe try to find a GL-AR300MD? They are discontinuted, but they were 58x58x25mm for a volume of 84.1ml. That's the only product I could find anywhere that met your requirements and is smaller than the GL-AR750.
Edit:
https://www.gl-inet.com/products/gl-ar300m/ (scroll to bottom to see GL-AR300MD)
IA link to when the product page still existed:
https://web.archive.org/web/20180113053817/https://www.gl-in...