Please note that the overlay used for CapSense sensors should be di-electric. Else, you will see false triggers or degradation of performance. Kindly check if you can change that.
I think you need to do some manual tuning to find the trade-off betwen requirement and over sensitivity. Please refer the Capsense manual tuning section 5 from the document below:
Please attach images of your board for more understanding.
Thanks and regards