Both Ricoh G900 and YI M1 have 20.0 MP resolution sensors but Ricoh G900's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and YI M1's sensor is Four Thirds (17.3 x 13 mm ).
Since YI M1's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Ricoh G900.
Below you can see the G900 and M1 sensor size comparison.
As seen above, YI M1 has a 8.0x Larger sensor area than Ricoh G900. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.