Since this thread remains active, I'll add my perspective that while the current Handbook does state the presiding authority (and visiting high councilors) should be invited to sit on the stand, there's no definitive language regarding the process for deciding when that might not be applicable. No specifics about who makes the decision, or who needs to ask who for permission. Seems to me that the presiding authority has discretion to make the decision about whether to sit on the stand -- obviously that should be the default, but to me it does allow for wiggle room if circumstances dictate the presiding authority be seated in the congregation on a particular Sunday.
And the other concerns about the effectiveness of presiding from the congregation as opposed to from the pulpit, remain valid. Regardless, he should always receive the sacrament first -- and while quite uncommon, there's nothing wrong with the priesthood holder passing the tray to that presiding authority in the congregation first, before others receive the emblems.
Perhaps I've missed something in the Handbook, if so I'm sure somebody will point it out
