There is no chance of a larger loop slipping off. Not gonna happen. Not ever. The only way it slips off is if someone doesn't put the loop over both horns after pulling through the center. Now, if you're just quickly lasso'ing the loop over the horns... then yes, but that's user error.
I have made, literally, well over 1,000 splices (some for fun, many for work) and I have never actually measured. But I'd say between 8" and 12" seems about right.
But, yes, we ARE overthinking that... we already have 4 posts on a subject that really doesn't need to be discussed. FYI, don't take any offense to that - I mean that in a "jesting" way