with shrap conversions im over 99%, but i have no intention to be 100% transparent about my loot or i would have already done so, its not the point, we are both off topic - im just saying that the above presented theory could be a possibility (maybe with different numbers) - i dont have the data to prove/disprove it just yet . while you have mainly data from using eff weapons that exceeded your looter profs.
When i was using unique legend war axe at 7% eff last year january (115animal looter then) i had about 97.5% tt return on 1 million ped cycled (108% after 400kped cycled) - of course with a weapon like that there can always be distortions and 1 million is probably not enough of a cycle for it but it opens the mind to the possibility that maybe efficiency and looter play together rather then separate.