But hang on. What if … what if I stack them atop each other? No that doesn’t work, the openings just cancel each other out, of course. But … BUT what if there was a gap between the layers? Let’s try that …
Nope, the backing plate and the main floating pane are not “connected.” Without that full sheet of acrylic, there is the added risk of pieces being pushed out and dropping inside.
So from the back to the front: there’s the main backplate, then a 1/4" wide spacer ring, then a 1/8" wide ring with the acrylic nestled inside of it, then another 1/4" wide front face ring. So there are two of the bottom-left pieces shown below.
For a good fit, I ended up making two almost-complete sets of parts, one set 0.010" larger than the other to account for the kerf. All pieces press into the back of the others and wedge in pretty tightly.