Thanks for your interest in DxOMark.
DxOMark score focuses on the sensor only. In the case of the EXR sensor, both modes available do not change anything on the sensor itself.
If EXR mode is activated, it only underexposes one half of the image. The pixel quality is not impacted. So on a sensor point of view the potential gain in dynamic is compensated by the loss in resolution.
In JPEG, and with a specific algorithm, some potential gain could be observed but we do not evaluate final images here.
The DxOMark team