In the diesel community we added sumps to the bottom of the tanks... that got every drop!
But still at fill up, you normally cannot top off without trying.
Just to clarify, a tank with a 20.8 gal capacity will never be topped off because of the air in the tank.
I know this seem obvious, but I want to make sure op realizes the volume of the tank does not equate to the amount of fuel you can put in once you account for vapors and vents.
Two things I've done, change the blade to a higher grade (Bosch Icon/Tricon) and polish the window with a wax/detailer spray to the point a microfiber glides on it.
So far so good, the only issue is the "haze", I call it hologram, effect until you polish it off.
I may try to loosen the spring...
Just to clarify we are ignoring the self tapping screw as a ground? Or will that be a separate thread?
I'm pretty certain by the shitty install and the unclipped zip ties that is a dealer tracker.
Fist off, thank you for your service.
Second, I think you need to focus on posting pics of the product installed.
There are several members that can help you with that as well as R&D and testing.