Hello Stefan,
A few things you can do:
Using inductance data along with moving average filter of 100 points seem to get you there.
Also, if you decrease the frequency of LC tank by a factor of 10, that will do the same effect. Or a combination of the two, if frequency cannot be reduced without reducing Rp below the minimum.
Another approach is to move your target closer - this will make the change in inductance more prominent.
And of cource, averaging on Rp data may get you there as well.
Please keep us posted on your progress, and don't hesitate to ask questions!