Ilfochrome is hyper sensitive to the different dyes in different reversal films. Therefore it takes different filter packs for each type of film.

If you are printing Ilfochromes, you had best stick to one type of film for your work if you want to stick with one pack, otherwise it is trial and error time just as in any other color printing.

Kodachrome is the biggest outlier. It will usually take more filter pack change than any other film due to the nature of the cyan dye used.

Best results are obtained with both color and contrast masking. This is due to the unwanted absorption of the dyes in the film and the paper and the high contrast of the pos-pos printing chain. It was not designed for optimum printing. Each of these masks is intended to correct for one of these flaws. They are used routinely in reproduction of slides for magazines, etc...