It can't be 100kwh battery for 360 miles because Model X has a 100kwh and an EPA of 348.
Assuming the Gravity will use the same battery modules as Air (very likely), the advertised 440miles is likely a conservative EPA estimation just like the Air promo of 500miles years ago (516miles after final tweaking and official EPA testing), the final Gravity GT range EPA estimation is probably closer to 454 miles with a 112kwh but no more than 122kwh battery.
If they're aiming for 360 miles EPA as the base, they'd likely use an 92kwh battery pack for base.