I think the idea is that larger sensors/image area allows for higher focal length lenses, which naturally have smaller depth of field. i.e. medium format hass

I think the idea is that larger sensors/image area allows for higher focal length lenses, which naturally have smaller depth of field. i.e. medium format hasselblads had a normal lens of 80mm, with a narrower DOF per f stop, whereas 35mm cameras had a normal lens of 50mm, with a larger DOF, etc. There's some curve somewhere that describes this.