MSP430FR2533: CAPTIVATE mutual capacitance with metal target

Hi David,
this is dependent on the setup, rather than dependent on the used capacitive sensing technology.
I'll try to make it as simple as possible:
All the technologies I am familiar with so far, do sense charge, not capacitance.
Thus the technologies are sensitive to change of the charge on the electrode/s.
For sake of simplicity looking at a plate capacitor with homogeneous electric field between the plates has a certain charge sitting on it's plates, which is dependent on the voltage applied to the plates, the distance of the plates and the dielectric matter between the plates.

Now coming to your question, starting with the most simplified case. Let's assume you're using our CapTIvate technology, measuring the charge of this capacitor, you get a certain measurement result in case without introducing the metal target into the space between the capacitor plates and thus into the electric field.
When introducing a floating metal sheet of infinite thickness in parallel to the capacitor electrodes, the effect on the charge and electric field will be 0. Why? Introducing the metals sheet in parallel to the capacitor plates means, the electric field strength at the spot of the metal sheet will be equal all across the metal sheet. Due to the infinitely thin metal sheet, what is of course not realistic, just for understanding of what's going on, the electric field will create charge on the metal shield. This charge will "translate" the electric field on one side of the metal shield to the other perfectly, by charges of opposite polarity on the opposite surfaces of the sheet. Thus no change in the electric field of the original plate capacitor at its plates, and thus no change in charge, no change in capacitance, no measurable difference. Thus no capacitive sensing technology will be able to detect.
Now let's modify this setup a bit, by starting increasing the thickness of the introduced floating metal sheet, still keeping it parallel to the capacitor electrodes. The translation of the electric field from one side of the metal shield to the other will happen the same way. But the difference now will be, the change of the effective distance between the plates of the capacitor plates will be smaller, by keeping the applied electrode voltage the same. Shortening the distance between the plates of a plate capacitor, while keeping the voltage and other parameters same, means increasing the electric field strength, thus increasing the charge, thus introducing a measurable and detectable difference.
Now this has been a pretty simple example, and the reality can be of course significantly more complex. But basically you can always boil it down to the "simple" question. Is the introduction of the metal target, you can even make it more generic, by asking is the introduced matter into the electric field of the sensing capacitor built up by your HW outside of the sensing/CapTIvate device influenced in way, which results in change of the charge of this sensing capacitor? If this is the case to a sufficient extent, you will be able to detect it with the CapTIvate device. If it does not have a sufficient impact, you will not be able to detect it.

I hope this helps you. In case of further questions, please let me know. In case these explanations have been sufficient, please confirm the resolution of your problem. Many thanks in advance.

Best regards
Peter