Leon,
I wouldn't say your doing something wrong as I need to rate my fp4 at 64 when I print on AZO. One must keep in mind the varibles that can be encountered i.e. light meters, shutters, water temps, etc. I know when I work I do everything the same every time maintaining consistency throughout the whole process. Everything works together as a unit, thus if one thing is not "right" it will affect outcome. On the other hand if that one thing is not "right" every single time in your working system your results will be the same and not necessarily the same as what other people come up with.