I took a different route...
My new to me 2016 had a drooping air dam where you could actually see light between the bottom of the bumper and the rubber air dam. I could tell there are two different materials, Hard plastic bumper and softer rubber air dam.
When I pulled back on the air dam, I could see that the gap between the body and air dam got larger. After putting the car on ramps I could get under it and see why. The air dam is only held in place at a few points. After several strikes, the rubber is stretched somewhat around the bolts in some area allowing it to pull out and droop down and not return to the original snug to the bodywork place.
I gathered some fender washers (large washers with small holes). I removed the air dam and cleaned the bottom of the plastic bumper and then used acetone and cleaned the rubber air dam. I re-installed the air dam using the large fender washers under the factory screws (I found 2 different lengths so pay attention if you do this) and used them where needed (mostly on the outer side sections). When done the air dam was back to making full contact with the plastic bumper.
Next, what I did that is unique (I think), I took some black silicone adhesive and pulled down on the air dam and applied a good bead of adhesive in the crack between the air dam and bumper on the front side. I let it set overnight to cure.
Why do this....... Why I did this was to add strength to the mounting of the air dam. Now when stuck by a parking barrier it will fold as designed and not deform around the bolt holes and sag due to larger mounting surface. Much stronger than original.
If it needs to be removed, I can simply remove all bolts, take a piece of fishing line between both hands and drag it between the bumper and the air dam cutting the adhesive and the air dam will fall off.