Where on the gas gauge is truly empty?

Go ahead.

 

When it hits E, I have around 6 maybe 6 and half gallons left

 

When the fuel light comes on, I hit the trip and typically go another 30-40 miles before filling up.

 

We'll let Shaq explain...
https://www.youtube.com/watch?v=EuH91bQXDuE
But in essentially You are dealing with a math concept known as the distributive property...No matter what you have to use x gallons of gas to drive from point a to point b and back. No matter what you do, when you fill or how much you fill, if you don't have x gallons of gas you will run out of gas. There is no "I'll use less this time and save money" you will always have to spend $Y dollars on X gas to drive Z miles. There's no way around it. Even if you filled up 1 gallon a day for 20 days or 20 gallons on day 20...you're still using the same gas and $$. The only way around this is if you were investing the gas $ in a short term high risk high yield fund. SO you could make 8-10% on your as yet unspent gas money.
IF you have a pizza and you cut it into 10 slices you don't have more pizza than if you cut it into 8 slices...

 

I have found I can drive 50 miles around the city after the light comes on without concern. I just reset the trip meter when the light comes on. The furthest I've gone is after the light comes on is 60 miles, a third of which was interstate, and I put 20.5 gallons in the tank that time.

 

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