If the parasitic capacitance (Cp) of your sensor is higher than 45 pF, then you would have to use manual tuning.
Typically, the capacitance added by finger (Cf) would be higher than 0.2 pF.
You design CapSense sensors in such a way that Cp is less and choose an overlay, such that the Cf would be high.
You can refer to PSoC 4 CapSense design
Cmod is required for the operation of CapSense to maintain AMUXBUS at a constant Vref.
Recommended value- 2.2 nF
You can refer to Section 2.3.2 of http://www.cypress.com/file/41076/download.