It's not about powder to bore. Not bore capacity(over/under capacity). The spreadsheet referenced is wrong.
It goes to the ratios such as demonstrated by those patented with the WSSM cartridges. These case ratios lead to different relative amounts burned within a chamber -vs- outside a chamber. And this does equate to a type of efficiency.
I'm sure Ackley described this in his patents, where Gibbs went a different direction.
I guarantee the weighting factors for WSSM cartridges are way lower than that of a 30-06 (just opposite of efficient).
The WSSM wide body high shoulder angles keep pressure in it's chamber(bottle-necking), where a skinny cased 30-06 with it's low shoulder angles shoves a slug of powder down the bore(funneling), adding to bullet mass, and igniting only at muzzle release.