Crossunder - 2 points for me:
1) Going below the PAPIs would surely STEEPEN the approach angle, unless you flare excessively and therefore 'stretch' the landing? A lot of PAPIs are set for long-bodies and should be ignored in small a/c in the later stages in favour of 'aiming points' once a safe approach has been established, of course.
2) AA v. LD is a matter of pure mathematics.
Taking an AA of zero (ie tangential to the earth's surface) and you go on for ever!
Taking an AA of 90 and you can 'plant it' veerrry accurately!
Somewhere between the two is the 'happy medium'. I don't think that needs to be in a manual!