Continuing the discussion from Call for ArM5 Errata:
Splitting out for discussion. This does need to be clarified.
Looking at the general size rules, we should probably be working with factors of ten, based on mass/volume.
In that case, if you have a base guideline for growth by a factor of 10, and adding another magnitude allows growth by a further factor of 10, you naturally take account of the size, based on the final product. Thus, there is no need for further adjustments for the size of the result, as there might be if growth were faster.
Going the other way, there is a question of whether we want it to be easier. If we do, then one magnitude for a factor of 100 is probably the way to go, with a base of 100. The MoH spell would need +2 magnitudes, and the HP one would need +1.
This would involve errata on the MuTe guideline, as well.