Margin - Options Vs Future

Using Zerodha Margin Calculator, I find margin for options (short) higher than future.

First the initial margin for options is higher equal to premium receivable and further option premium receivable itself is blocked for margin.

Thus, option premium receivable seems to be double counted for margin even as risk profile for future and option (long future and Short put / short future and short call) is roughly same.

Therefore, if option premium is already added into the initial margin, the same should be available for use and not further blocked for margin.