Quoting myself from Jeff Knoll's old forum:

In a Cretor's 20 oz kettle, we found the true pop-out of a bag of corn rated at 70 was more like 22! The difference? Instead of using the tube measurement, we put the corn in the bags being used to serve the customers.

The tube measurement is not real world, but only a comparison.

Some other factors that were a surprise-

Every bag is labelled with a nominal capacity. Sometimes the capacity is based on the bag being opened to a rectangular shape. Ever see a rectangular bag of corn? They tend towards cylindrical. You might want to do some testing of your own. We found that one of the smaller bags held half again as much corn as it was labelled for.

Oil. The more oil you use, the lower the pop-out ratio. We found that 6 oz of oil was the best amount to cook the 20 oz of corn evenly and not shrink the yield. Using 8 oz substantially reduced the pop-out.

Factors like this can increase your popcorn costs, and too much oil can make customers shy away from your corn because of smaller, greasy kernels.

code:

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                         3-plex    6-plex    20-plex    average
lbs corn : lbs oil        1.9:1     2.6:1     3.4:1      3.07:1
lbs corn : lbs butter     5.0:1     4.5:1     6.5:1      5.89:1

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In my opinion, the three-plex had wet, nasty popcorn. The six-plex had tasty popcorn, but the customers liked to drown it in butter. The 20-plex had dry popcorn and charged extra for more than a couple of squirts of butter on the top.

IIRC, the target numbers were 3:1 for oil and 5:1 for butter.

I didn't analyze salt because these theaters didn't order it enough to get a good result. I would have had to analyze about 7 years of data to get a good number. Besides, it was common practice to use salt to soak up spilled coconut oil, for some reason.