The esk8 calculator shows a maximum theoretical top speed of 23.62km/h. Is there anything that could make that calculation inaccurate other than going downhill?

The calculator calculates 6s as 22.2v which is nominal and lover than fully charged 25.2v, the efficiency should be set to 93 %, i dont know why is it so low as default. Enter 7s battery to get a speed calculation on your full battery. Then you get 25.63 km/h