Voltage at the capacitor should be close to the input voltage. Too-much of a voltage drop will make the motor labor when starting.
When the voltage goes way down, then the motor won't start. Capacitors in parallel are used for lack of space at times. When they are parallel you add the MFD's to get the total MFD's capacity, just like a car battery amp capacity.
When the capacity in MFD's is right, you should see a little voltage drop. There is a formula to determine the size of a capacitor in a circuit.
If you get stuck let me know. Guido.