Low-Fuel Indicator / Distance to Empty (math involved)

[KensAudio]

Once upon a time, someone called into CarTalk to see if it was okay to run his fuel tank dry in order to know exactly when his low-fuel light comes on. I figured out a way to do the same thing mathematically, and wondered if anyone else had similar results...

1. According to the manual, the tank on my '03 holds 16.9 gallons.
2. I just filled up today: 14.911 gallons (did not 'top off'). This means there were 2 gallons of fuel left in my tank.
3. I had zero'ed my 'B' trip odometer roughly when the light came on, and that was 31.8 miles prior to the gas station.
4. According to my 'A' odometer, I'd traveled 417.1 miles since the last fill-up (again, no topping off), so 417.1 / 14.9 gallons = 28 MPG (This makes me happy, but not the purpose of the post.)

31.8 miles / 28 MPG =~ 1.135 gal used since the indicator came on.
Add the 2 gallons that was still in my tank, and I get approximately 3.1 gallons between the indicator lighting up, and the tank being empty.
Multiplying that by 28 MPG, and I get (theoretically) about 87 miles of range after my light comes on. I've only ever pushed it to the high 30's or maybe 40 before filling up, but my question to the group: Does this sound right? Has anyone else found a margin of 3+ gallons between indicator and dry tank?

Notes:
1. While my long term average for a tank might be 28, I certainly can't assume that that value is accurate for the last 31.8 miles.
2. I don't know if the book value of 16.9 includes the volume of the pipe between the gas fill and the tank itself.
3. I know variations in temperature can affect the density of the gasoline, but I don't claim to know the formula or the extent. I didn't track the temperature when filling up the last 2 times (or ever).
4. Since I missed exactly when the light came on, the 31.8 value could ostensibly have been higher - but not likely by much more than a few tenths.

I'd like to see, statistically, if enough of us do similar math for a little while, perhaps we can get enough examples to narrow in on this. And, none of us has to run our tank dry to get a rough result!

Thoughts?
- K