I'd say it's time to pickup a shade for your tablet/smartphone. I wouldn't be caught dead without one on a bright sunny day.
There is no way to determine max setting with the printing on the filter rings. What you can do is grab a dark towel or sweatshirt and head outside with your gear.
Make the sign of a gun with your index finger and thumb. Point your index finger towards the sun and rotate your thumb left to right along your the axis of your index finger. Where your thumb points to is direction of the max effect that you can attain from your polarizing filters.
Point the camera of your drone towards the direction your thumb pointed to.
Have a seat next to your drone and cover your head and remote with the towel/sweatshirt so you're in the dark and can see your screen.
Reach out and slowly rotate the adjustment ring of your filter keeping an eye on your screen. You may have to go back and forth like focusing an old manual focus lens. Stop when you notice the sky/objects darkening the most before starting to lighten up again.
Take a Sharpie marker and put a witness mark on your drone's camera housing and on the the fixed and adjustement rings of the filter so that the marks all line up.
The next time you go out to shoot, after you screw on your filter, check the witness mark of the camera housing to that of your filter. If they're all lined up, you'll be at max setting without having to waste time fiddling with the filter and screen trying to get the best setting.
To reduce the unbalanced dark/light sky issue when using polarizers, reduce the amout of polarization by about a 1/4 turn in either direction. You still get decent polarization to cut glare off water etc and the skies look more even.