Zeiss Calypso and Manually Setting Grey Value

Hi, everyone. I’m using optics with backlight to measure the radius of a part. However, due to poor fixture design, the rotation of the part is not stable. Because of this, sometimes the side of the part is visible. This causes the measurement to be taken on the side rather than the top edge of the part. This part is made out of liquid silicone rubber, so clamping it in the fixture to help set rotation is not possible. We also use a 64 station fixture, so it wouldn’t be viable to manually set the rotation each time. I have thought about manually setting the grey value. This way the measurement bypasses the side of the part which is dark grey and hits the top edge of the part which will have a much lower grey value (almost black). Is this a viable solution? Does anyone have resources where I can learn more about setting the grey value? Thanks!