No one in the "pimp spot" has been voted off the next day in the 5 years of the show (until it gets down to 3 people left).
Do you think if they gave it to Ace, it would help him? ;)
The producers want to end each show on a good note--literally. So when they watch rehearsals they probably save one of the best, or the best, performance for last.
If somebody sucks, they're gonna suck no matter what spot they have.