Sandwich case and pcb design

When designing for a sandwich case, what’s the prevailing wisdom on the size of the pcb - should the main pcb be the exact same dimensions as the case plates, or smaller to have the main pcb “inset” from the case?

Or is this a personal preference type of thing? (I am assuming there’s lot of personal preference involved here :grin: )

I’m new to keyboard design/layout so not sure if there are some “normal” conventions. From looking at output from I am a bit confused as to how the “open layer” and “closed layer” fit together. “Open” appears to where the usb jack would go. Is “closed” usually a “ring” around the main pcb?

Is it typicaly to have the USB jack on the bottom of the pcb?

Googling some pictures of sandwich designs, it seems that a ring around the pcb layer is typical.

The PCB is almost always smaller so that you can use stand-offs to create a simple two piece case, or a multilayer acrylic case.

Good example and explanation can be found here:

You may also want to watch some build streams of the 1Up Keyboard sandwich cases on Youtube, or the Perry60 V2, etc.