> I think the plastic lens mount might be obstructing the light going to the sensor

It's actually a low-profile, 3D printed thing housing a glass UV/IR cut filter. The housing is flush with the glass filter unlike the stock Pi HQ camera lens holder. Removing the UV/IR cut results in full-spectrum photos that manifest the same color shift problem which is characteristic of CRA optimization (where they deliberately put the microlenses off-center toward the edges of the sensor.

> As far as I can tell, there's no lens array on the sensor[1][2]

I thought there is a lens array on almost all Sony sensors? [2] for example lists a "CRA characteristics of recommended lens" section on page 47, but this is not the full datasheet and only goes upto page 25. I can't find the full datasheet on the public internet unfortunately.