Both Pentax K-3 III Mono and Ricoh GR IV have APS-C sized 26.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another similarity between these two cameras is that both Ricoh GR IV and Pentax K-3 III Mono sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the K-3 III Monochrome and GR IV sensor size comparison.
Sensor Size and Resolution Comparison image of Pentax K-3 III Mono and Ricoh GR IV Cameras
Pentax K-3 III Mono and Ricoh GR IV have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Pentax K-3 III Mono
or the
Ricoh GR IV ,
including hyperfocal distance.
