You'll find the main aim of this technique is to shade the recesses. If it only shades the crevasses and low areas, then it is doing it's job well. However, you should be getting some colouring of the flat areas too. If you are not, then it is possible that the paint you are using may be too thin. Also, keep in mind that I used the citadel washes to finish off the weathering effect, so this may be what you need to do to finalise your painting. The dip will add the dirt, the wash creates an overall darkening of the entire effect. Another thing you can do, is once you've dipped a few times, if it's still not doing what you expect, paint some of the wash onto the areas you want messed up some more. This will add time to your project, so I do recommend using the washes over those areas instead to reduce the time it takes.