levels of essence action - which essence type is best for a given problem?
It's horses for courses. A problem at level 2 is best addressed by a flower essence or even something from the range of vitamins and minerals. It would be silly to use, for example, an OriginalAA Root essence here, it misses the mark entirely and might stir up deep stuff that has little if anything to do with the problem at hand.
A deeper acting essence is only better than an essence with shallower action if that deeper action really is necessary. By contrast, a problem at level 7 might be treated using an OriginalAA Root Essence, a Falling Leaf, Seed, or Tree Bark Essence.
An alternative approach is to use combination essences such as our sixteen Quality Essences which have a wide range of essence families discussed above within them to support inner growth. This means that they are able to act at the appropriate level, be that shallower or deeper, according to need.