I'm developing a measurement system for optical sensors. The alignment error of the sensor in the test fixture causes a component of gage error that is proportional to the true value of the sensor response when alignment is perfect. For example, if the true value of one sensor response is 100 counts and alignment error adds another +/-10 counts, then another sensor of true value 200 counts will have an alignment error of +/-20 counts. This kind of measurement error doesn't typically happen in measurment of mechanical components. All of the discussions of gage R&R that I have seen assumes that gage variability is a constant whether you are measuring small parts or large parts. For my application, the largest contributor to gage variability is a function of the underlying values I am trying to measure. I can influence my gage R&R results by selecting only weak or only strong response sensors. Is there a way to characterize the variablity in my gage that that avoids this problem?