Each person is individual, has different sensitivity levels, and many other contributing factors that make their needs and responses different from others. Because of these differences, we can't tell anyone specifically what they will need to do to have Spooky effective for them without being too strong, etc. Many of the "complexities of Spooky2 are settings to allow the user to change settings to fit the product to their needs, etc.
All of this to tell you, and anyone else, that you can adjust the amplitude (voltage) setting as necessary. Some users use remote voltage as low as 2.5 volts, as they are sensitive to a higher voltage. Some set the same value to 9.5 to 20V for other reasons. Remote voltage has a very wide effective range, but it is up to the individual user to use the device within parameters that are effective, but not too uncomfortable or harmful for themselves.
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