I would not trust any measurement made through the top. You will have to remove the cover to change it anyway. The proper way to set the level is with the top off. The level should be 5mm from the top of the bowl. The measurement should be to the surface level and not to the miniscus.
To do the measurement you should disable the ignition by pulling the small connector from the ignition box. Put one finger over the float axle retainer spring (it is normally held by the now removed top). Have someone crank the engine till no more fuel comes into the bowl. At that point the level should 5mm below the top surface.
Bosch Master, ASE Master, L1
33 years MB technician