Your problem is that your fuel guage is obviously not broken-in yet. A properly broken-in MB fuel guage, and anyone else correct me if I'm wrong, will read accurately from 1/1 through about 1/2. After the actual fuel level goes below 1/2 it will do one of the following:
a) erratically jump all over the lower half of the guage;
b) stay at about 1/4 until the car runs the tank dry and you stop;
c) bounce back and forth between two distinct level readouts, causing you to wonder, "Which one of you is it!!";
d) any amusing combination of the above three.
You probably have another year or two before you see proper level indication. Enjoy the time you have until then.
tongue only partially in cheek,