Gentlemen:
The correct way to prepare any volume to volume solution, in this case glow fuel, is first to add the lower concetration components ( as already been calculated) to about 1/3 to 1/2 of the methanol volume in a reservoir into which a mark to the 128 oz ( 1 US Galon in your case) capacity has been done. Then you mix what you have added so far, and continue adding the methanol, mixing while adding it, until you reach the 128oz mark done to the holding jug ( or whatever you use) This is the correct way of doing any volume to volume solution. There could be molecular attractions ( or repulssion) between the liquids that could cause you to end up with a little more concetrated mix( or a less concentrated mix) than you want if you go by the mathematics only way. While this may be a small deviation, you may save some $ . I think that comercial manufacturing uses a convertion and prepare the fuels in a weight by weight system because is easier and more accurate concentrations can be achieved. My 2 cents of chemistry. BTW I mix my own fuel, but use the metric system which is easier and basicly error free.

Angel Ramos
Arecibo, Puerto Rico