WTH Balancing coefficient for solar production returned to grid

Final energy bill received form energy company in many countries depends on a returned to grid coefficient. We can treat grid as a storage but can get in case of Poland: 80%(<10kW installations) 10kW) or 70% (>10kW installations) of what we gave. This affects the gauges not showing this dependency hence we don’t know where we are with production versus actual bill.