Apparently Fenix Uses 77kg for crew members (pilots) which is a standard ICAO/EASA value IIRC, and 80 for pax, which again is somewhat standard in ICAO/EASA (pax weight calculation varies depending on the type of operation). If you put 0 pax you’ll have 154 of weight (2*77), if you put 1 pax you’ll have 231 kg and so on.