Indeed, 'efficiency math' isn't about process as much as it is about equipment, with one caveat: the mash.
First, you need to fully convert the mash, that is at that point 100% efficient.
I think many folks are mashing by time, not gravity or % conversion, hence their lower numbers. Out of the mash-gate they are already taking losses.
Once you focus on 100% conversion in the mash, you start focusing on other effective factors, like temp and pH. You might increase your time initially trying to convert, but you could be at it for days if the pH and temp are not right. Understanding the temp and pH ranges of the various enzymes will help nail conversion consistently and without excessive time involved per brew day.
After the mash though, and assuming 100% conversion, losses in efficiency are all down to losses of volume. Anything left behind is not going into the fermenter and thus has no chance of making it into the packaged beer.
This is why I pump 100% of my kettle to the fermenter, trub and all. Brülosophy has repeatedly disproved the "clear beer in fermenter = clear beer in glass" myth. It is quite the opposite. That practice alone is costing folks efficiency and they are just throwing away both sugars to be eaten by yeasts, and important nutrients and other goodies for the yeast to properly flocculate and eventually drop clear. (not the least of which might be whatever kettle fining agent used, if any, that will still do its job in the fermenter, but not if you hold it back and trash it!)
I've seen folks use both kettle finings and yeast nutrients at the end of their boils, then whirlpool to pile up trub and keep it out of the fermenter. Do they know how much of those finings did the job if at all by that point? Do they know how much nutrient made it into the fermenter and didn't get attached and dragged down into the trub pile? And yes, then they wonder why they still had fermentation issues as if nutrients were too low, and their beer takes forever to clear, but I digress...