Fuel tank capacity question

This summer in the JKU driving across Canada I was going through a very rural / desolate section of Ontario in the NW and reached the point where I had about 100KM of fuel left according to the EVIC DTE calculator, so well before the light even goes on.
Pulling up the GPS I tapped the handy 'Where am I' and the 'Fuel' to see where the next gas station was and saw that the closest station behind me was 50+ km backwards and a no name brand, but that there was an Esso ~35KM ahead and another station about ~70KM ahead, so thought just keep going and grab it from the Esso....
Well the Esso station had recently burned down, and the second station had gone out of business, now I had been on 'low fuel' (stops showing estimated distance when below 50kms DTE) for a while and the closest station was now another 57KM away, and rough calculating that was about 25+KMs past the initial DTE estimate.

Eventually rolled into the Big Flying J Shell station white knuckling it the whole way for the last 50kms trying to 'Hypermile' a Wrangler with the top down (wasn't sure if pulling off highway to close top to improve aero would cost more in momentum and acceleration to get back to highway speed), was super relieved.

Finally filled up the tank at what was essentially 25+KMs beyond the empty estimate and then pumped 'til it clicked off at 81.9L (no I didn't do the wait and refill since the flying J was about 5c/L more expensive than other stations, so it likely coulda taken a little more too) but just from that first click alone there was less than 3L (less than 1 US Gallon) of gasoline left in the 85L tank plus whatever is in the fuel filler hose or whatever where/when it clicks off. I'd never been able to fill up past mid 70s even when I knew I was 'empty' in town waiting for gas prices to drop 30%, so definitely was well beyond the typical 'E' empty.

Likely not good on the fuel system to go much beyond that level where the fuel pump might not be submerged, or it might start sucking air on an angle, etc.

Never want to go through that again as it takes all the fun out of the road trip, but glad for the buffer beyond the DTE calculator and E + orange light indication of empty instead of being stuck in the wilderness (even if a highway runs through it) with no ammenities nearby when those unplanned overextension of resource occur (like being stuck in a winter traffic jam).

So it seems like there's a little more than 7L / 1.8Gal past the empty estimate left in the tank from my experience, but of course your mileage may vary.