With certain ingredients, if you make a recipe that produces one of that ingredients effects, the effect is changed in some way. A notable example is Giant's Toe- if you make a recipe with the "fortify health" effect the effect lasts longer and adds more to the vlaue of the resulting mixture (usually a fortify health potion, since the name is determined by the highest value effect).
I've usually heard it referred to as an value / magnitude adjustment, but I guess you could all it a "priority factor" because bumping the value of the effect up or down can make it (or some other effect) a higher "priority" when it comes to determining the mixtures name (and hence whether it is a poison or a potion).