B404X Base PCB Components On Backside of PCB

Hello,
I am creating a base PCB for the Particle B404X SoM. To save space I am putting power supply circuitry on the backside of the PCB, with the B404X SoM on top. A tutorial said not to put components underneath the SoM but it's okay to put components on the backside of the PCB. Can I put surface-mount power-supply circuitry directly underneath the M.2 connector or the SoM on the bottom-side of the PCB? I'm making a 4-layer board.
Thank you

Yes, the back side of the board underneath the SoM is OK.

It's just the area directly underneath the SoM on the same side as the M.2 connector that you should not place components because of the limited clearance between the shield on the bottom side of the SoM and the top of the board with the recommended M.2 connector.