My gas gauge only reads half full when the tank is completely full. It goes to empty rather quickly and shows empty when it's half full.

I tried to take out my sending unit but it wouldn't move (I only had a screwdriver). When I was under the car I realized that my sending unit doesn't have a ground strap to the fuel line. My rubber fuel line is rather long too - about 12". The sending unit seems to have metal to metal contact with the tank via the tabs - is that enough to ground it?

What's more likely for my gauge reading only half issue? a bent arm on the sending unit (no clue if it's a repro unit or not but it looks old)? half sunk float? missing ground strap of sending unit?