Could have had something to do with dual exhaust, but not sure.
That crossed my mind too, but I don't have the extensive knowledge of these cars like you guys do.
My best recollection is that it was in the top hole on my car when I took it apart, but my car was a single exhaust and I'm converting to dual, so that really doesn't help any. I also tried screwing the bolt into both holes, and wouldn't you know it, it easily threads into both! So that doesn't do me any good either.
The assembly manual shows it going into the top hole. But if this is indeed a single vs dual exhaust difference, then that probably doesn't help either. It's interesting that there are 2 holes on the drivers side and neither on the passenger side. This might help to indicate that it is a single vs dual issue as there doesn't seem to be anything that would use the other hole.