Not really that precise; those are really big margins (look at the numbers), and they're basically just general rules for relatively accurate mids and god treble extension. Also, I should say that these are rules that I made up --- based on all the reading that I've done (there is lots of reading material, but it's everywhere and there's no "Bible for IEM Design", so you'll have to synthesize it together yourself), and the hundreds of IEMs that I've heard. If you ask an IEM maker whether these "rules" are good, they'll say, "Yeah, but it's hard to achieve". These "rules" are more like ideals. I'm just giving out general principles of sound acoustic design.