This is a part of running BHO that tons of people have questions about, and the answer still isn't 100% known.
However, first you have to think about whether you are willing to sacrifice the qualitiy of your BHO for a little extra BHO.
For example, i have a tube that holds 1 ounce of broken down nugs.
I can run 1 can then a half if needed through, and get about 5 grams of pure nectar.
If i were to run that extra half a can, or another can, i risk over blasting the material and getting more than just the precious trichs.
You risk getting Chlorophyll, plant waxes, and other plant matter into your oil, degrading the quality, the more butane you run.
You run a higher risk of getting these impurities in your oil if you grind your material before running.
I would run 1 to 1 and a half cans of butane per 1 Oz. of material to ensure quality.
To maximize yield i would focus on making sure your tube is packed correctly, evenly, tight but not too tight.
Also a big factor to yield is the starting material, If your bud has large trich heads or small trich heads, and the amount of trichs.
Quality in and quality out, it is not worth sacrificing quality for quantity.

Goodluck!
"Formal Education will make you a living, Self education will make you a fortune."