One reason you may feel it more on the palms, is that due to the thicker skin in the hand vs. on the back of the hand is because the current is mostly going through 1 smaller point in the skin, so more current in a smaller location causes more sensation. This doesn't mean that it is better for you.
Generally, you want the frequency signal to be spread out as much as possible to cover as much body volume as it will... The more volume it contacts, the more chance it has of contacting pathogens and destroy / disable them.
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