In my experience, Nissan seems to want you to think you have far less battery remaining than you actually do. I find it falls mostly linear until about 50% than far faster until about 10%. On several trips I've seen the GOM drop to 10%, rise back over 20% then very slowly drop back down all while driving at consistent highway speeds. Leafspy readings seem to be consistent throughout and at 2% on the GOM, Leafspy was still showing 6.4 kWh remaining. Here are some stats from that trip - my most inefficient one yet!
Conditions: -29C (-20F), dark, 15 kph (9 mph) crosswind, mostly flat terrain, 106km (66mi) round trip, average speed 75 kph (47 mph)
GOM: 100%, 174km (109mi)
Leafspy: 34.8 kWh available, battery temp 2.2C (36F)
GOM: 2%, ---km, very low battery warning
Leafspy: 6.4 kWh available, 29.8 kWh used (I know, the math doesn't add up!), battery temp 16.3C (61F)
Efficiency: 3.56 km/kWh (2.22 mi/kWh) => calculated range of 124km (77mi) based on original 34.8 kWh indicated by Leafspy and assuming it would keep going to 0 kWh indicated.
2018 Leaf SL, 43,577 km, SOH - 92.16%, Hx - 119.23, AHr - 106.39
2020 Model 3 Performance, 9,581 km