It's only about a 20-30% speed up, so it's not some huge problem if someone uses a different n.  But sure, we could add a comment about it in case someone uses something else.  Also, the speedup gets less as n increases, so n=9 probably isn't too important.  I was more concerned that someone would use an even n.  Is it just tradition to use odd n?  Or is there a fundamental reason that we always use odd values?