On full sunlight, cloudless days it is recommended that the sensors have a top hood/cover over them so the skyscreens are looking up at these covers rather than the blue sky.
I'm surprised the covers aren't supplied as standard equipment with the CED M2. If they are, you should use them on the sunny cloudless days.
The covers with my Oehler are an orange-colored plastic. The covers for my PACT are white plastic. When it's cloudy out, I don't use them. I do use them on the bluebird days.