Capacitive touch screen sensitivity question
You need to continue your equivalent circuit to include the device. There is a series capacitance to ground inherent in the device by virtue of its size.

The parameters you have on your equivalent circuit shown are not significant, the dominant one is the capacitance to ground of the human - it will be about 100pF, much smaller than the ones within the body.

The stylus may have a capacitance to the screen of about 1pF. At 100kHz this is a reactance of 1.5Megohms - this is much larger than the level of resistances found in the body.

Touch systems in phones and tables use frequencies in the range of 100-500kHz.
What type of device is it?

Something the size of a cell phone will have about 4pF to ground when it is not connected to anything, a tablet may be double or triple that.

If the device is connected to a charger it will gain a large capacitance to ground through the charging cable.