Fuel line routing question

[Toledo Jim]

Problem fixed but still confused.

Original problem, Out of gas, no RES or Prime:
What I found:
1: Running with petcock in ON position.
.     a: hose from RES at tank hooked to ON at petcock.
.     b: hose from ON at tank hooked to RES at petcock.
.     c: tank takes 3+-.1 gallons to fill when quits (twice) should continue to draw from "reserve gas" at this time until empty, right?

What I did to fix:
Switched hoses (at frame petcock) and ran on RES for additional 30 miles, took 3.6 gallons to fill tank. (Indicates to me RES outlet at tank is not blocked.)

Result:
Now operates correctly. (Petcock in ON position, 165 -175 miles on tripmeter, sputters and surges, switch to RES and go to gas station)

My question is:
Why did it quit in ON position when hose for ON at frame petcock was hooked to RES at tank outlets? (Seems like should have emptied tank?) :dunno:

[scratch]

Fuel consumption variation. You still ran out of gas, but maybe you hit too many lights on your commute. We're talking about a .5 gallon difference in fuel consumption, which would be about 30 miles, or an 7mpg difference (165 miles/3.1gal=53mpg vs. 165mi/3.6gal= 46mpg).