@erhanevgin most Meraki switches only use front rails to mount them, but MS355s use front and back due to the weight of the power supplies. As we only use 120, 210, 220, 225 and 355 I cannot be sure where the rear mounts start, but I'd hazard a guess at MS250 as they have the hot swap power supplies. I'd guess that 450s are designed for four post 800mm deep racks.
We do have two sites where we only have 600mm deep racks with MS355s and we found we could install rear rails and use a 1U cable management bar as a rear support for each switch. Handily it also guides the power cables 😎