Where I have my MES is on my covered front porch.
And the only time the Sun affects my MES 40 is in the Spring, Winter, and Fall, because then the Sun is low enough in the sky to shine through the Smoker door Window onto the sensor on the back wall, fooling the MES sensor into thinking the Smoker has reached the heat setting, and shutting it down at a lower actual Temp.
So when it's sunny out, I lean a piece of plywood on the front of my MES, except in the Summer when the Sun is high in the sky & can't get to my smoker window.
That Heat deflector doesn't hurt anything. Only things that cover most of the width of the smoker effect it. There has to be a couple inches of open area all around, and some in the interior area. This is usually when people cover too much with Foil Pans or foil.
I once had 2 foil pans on one rack, both 9 X 12, and my heating was all screwed up until I moved one.
Bear