Where does the final approach begin if the glide slope is intercepted at an altitude above that depicted on the approach chart?
The FAS begins when you've intercepted the GS, and are at or beyond (below) the charted GS intercept point (altitude).  So if your charted GS intercept is at BONGO at 3000' and you intercept the GS outside BONGO at 4000', your FAS begins at BONGO.  If ATC has you join the localizer at 2500' and you intercept the GS at 2500' inside of BONGO, then that point, where you intercepted the GS, is where the FAS starts on that approach that day for you.

There can be lots of ways to say that, some of which are less clear than others.  But that's the simple, and hopefully clear, answer.  And, maybe, going back to the FAA definition, you can see how what they put on paper matches this concept as stated here.