What nworth said. The recipe ilford presented was tailored for ilford's offerings. This is why I make a hypo solution an add it at developing time, if required at all. You need to build up enough developed silver first, and that will be different with each type of film. I do not put any pre-mixed in the developer for that reason. Just have a look at the tables I posted on my blog.
I shoot a bunch of frames ranging from 25 to 1600 iso in 1 stop increments with a card indicating what iso I am shooting. When I look at the developed strip, it allows me to guess how much more (or less) hypo to add. You need to take a more systematic approach to nail it down.