The question is what is on the box. There are apperate with 27mm installation depth. It worked well for me. You know whether it works if you calculate the thickness of the shelley + the installation depth of the apperate - the depth of the can.
That's why I always use slightly deeper boxes. e.g. universal box from hsg. You can simply drill out the old one ;)

Extremely small for a complete disturbance control with klemen and web server! You wouldn't believe what you can squeeze into a can with a little imagination 😂