In practice, you must determine the best level of dye by trial and error. I always do a concentration series.

And, the amount varies from emulsion to emulsion and of course if you want J aggregation it takes 2x the amount, however if aggregation is going to take place it will and may only cover 1/2 of the emulsion. Therefore it is best in this case to optimize for the aggregate to form rather than some sort of mix.