I think it is great that you go on an electric car forum to as questions about a gas powered cars gas tank issue!!!
Well, the "empty gas tank issue" has been around for a very long time.. I would say 60+ years. Auto makers do not want to get complaints that their cars run out of gas and strand their customers.
Also, the saying goes that "Nothing is fool proof because fools are so ingenious..." I think this issue is especially true nowadays, when we see digital displays, and expect exact levels of precision.... So my explanation is as follows.
The fuel gauge is not a precision instrument, it gives a "general indication" of how much gas is in the tank. In addition to it not being a precision instrument, the car companies have ALWAYS built in an extra number of gallons AFTER it shows empty. This is so that those silly drivers that don't think that fuel gauges apply to them can reasonably get to a distant gas station before the car dies of starvation...
Be happy that you have those extra gallons for an emergency some day... Either way, you should never let the gauge go below 1/4.... It is not good for the gas tank, and not good for the fuel pump that relies on a full tank of gas to cool it.