Hmm.. just happen to saw this.
Well, add some info about superior alchemy.

Superior alchemy is 100% based, mean if u x+y+z, u will get x/y/z only.
However, the exception is, if x+y and x/y doesn't not exist in compound range, even it is 100% based, it will be a random result with the main based, example x or x+z. (Apply in all alchemy)
Lets look into primary/junior, if u use x+y, u will get x or x/y.
While for superior, if x+y does exist within compound range (need +3/4/5 rank) to get it and there is no others same based in -7 rank~0 rank, the result is either u sucess +3/4/5 or get rank 1. If an item or more exist within -7 rank~0 rank, u will get that, count as fail.

Good luck =)