I'd bet on there being a problem with one of the senders, but if you want to rule out a problem with the instrument panel, you could try putting your own resistor in the circuit to simulate a different sender reading.

I don't know anything beyond my 2001 3.0i, but here are some notes from when I was debugging a problem once (I don't think I had any problems other than a code the Foxwell was giving me - D7 IKE: Tank sensor 2 (without fuel pump), and Foxwell also said both sides were giving values that were too high; I never figured that one out):

Sender resistances with a pretty full tank:
Left: 481 Ohms.
Right: 474 Ohms

Voltage at disconnected plug to left sender:
12.0V

Voltages measured at the disconnected plug to the fuel pump assembly:
12.0V (going to the sensor)
13.0V (going to the fuel pump when activated; engine was off, battery charger on at 13.3V)

I think those can all be considered reasonably nominal values with a full tank.

So for example, if you were to unplug the connector and put a 100 Ohm resistor in place of where the sender would be, the fuel gauge should respond. High cluster readings from Test 6 should change as well, maybe not damped as the gauge will be.

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2001 X5 3.0i, 203k miles, AT, owned since 2014