Fees

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Fees will be paid as a proportion to the option premia.

$$FeesPaid=FeesProportion*OptionPremia$$

The OptionPremia is without fees and after the volume impact.

The FeesProportion is a proportion the user pays for buying/selling option, on top of premia.

There are other alternatives for paying fees, like paying proportion of excercised value. But having fees as proportion to option's premia is the easiest to understand.