Usable fuel level

I saw a post recently about this but couldn't find it now to respond.

My 2016 Roadster has a tank capacity of 23.5 l according to the manual. The manual says when you have 3 bars on the guage you have 4.5 l left in the tank.
I ran the gauge down to one bar which tells me 25 km range -(stupid for an ex pilot I know - woulda been fired for that) and then filled up to the silver cage in the filler neck so that just the bottom of it was covered with gas.

It took 20.3 liters meaning that I had about 3.2 liters left. At my average burn rate of about 7 l/100 I should have had a range of about 43 km which means that either the gauge isn't super accurate(probably) showing 25 km or the factory is smarter than I thought and accounted for the unusable fuel of the last 17 km (42-25) worth which would be about 1.7 liters unusable.

Either way, it seems I can run to one bar and 25 km showing in the range and expect to keep going for that 25.

When my estimated range goes to zero, I have 1 gallon left in the tank. That's what I go by, and it's been repeatable. I zero out one of the trip meters when I hit zero estimated range so I can manage my last gallon. I don't like to go that low, but sometimes it happens.

Hoopla

low light came on with 165 spirited ride miles 4.03 gallons put back in not to bad I feel considering how I rode yesterday only 130 miles today