I don’t claim this answers everything, but it does very clearly explain why some people “see” no signal loss at all while others “see” a huge drop.
[UPDATE:] What I find fascinating isn’t so much the obvious emphasis on a supposed good signal, but rather the total deemphasis of a medium signal. I mean, look at that sliver for three bars. Apple goes from “you’re fine” (4-5 bars) to “you’re not so fine” (1-2 bars) almost immediatley. It’s as if they never want you to think that you might be fine.