A possible approach to the flare test would be to mininize the variables in the test. Lock down the camera with the target facing the sun. What ever the camera settings, they shouldn't be touched again during each part of the test. Obviously you should attempt to place the metered exposure at an exposure of 8 / ISO. Meter a gray card and open up 1/2 stop. The target should have have a sufficient range of reflectance to represent an average luminance range.

Shoot the target that has the background completely blacked out. This will not produce zero flare but it will be greatly reduced. Remove the "flag". About 1/3 to 1/2 of the frame should be sky. Shoot the set-up. Include a sensitometric strip in the processing of the test.