The issue with handlebars is that they can act like a tuning fork, thereby causing numb hands. The purpose of the weight is to change the resonant frequency characteristics of the bar and the location where the vibration is least to where your hands are placed.
In plain english the amount of weight required is the amount that works (statement of the obvious). It really can be hit or miss. Moving the bar slightly from side to side (one side ending up being slightly longer than the other) can also have an effect (good or bad). I wouldn't stress too much about weights being different on each side. If you don't notice anything wrong, then you're good to go.
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