If one were to fall far enough to take damage and no magic or other defense were used, is there a Form that would help provide a Soak bonus, at the normal rate of 1/5 the score?
The three that come to mind would be Auram, Corpus, and Terram. Of those I'd say Terram has the most merit, but still not certain.
I'd use Terram, although a case could be made that it depends on the landing surface. For example, I might be convinced to use Herbam if the magus fell unto the deck of a ship.
Terram also covers the property of "hardness", so it could be argued that no matter the Form of the surface, if it hard enough to do damage than it is its "Terram property" that is causing damage.
For simplicity's sake, I would probably keep it Terram.
Sounds good, I was figuring that myself, after all if a rock falls on a Magus Terram would give some soak bonuses. It's just the circumstances of the Magus falling that put a slight wrinkle in it. Using Herbam for wooden surfaces (or even Animal or Aquam) would also make sense depending on what's being hit. A catch-all of Terram keeps things simple though.
Auram also makes sense to me for a general form, because of the "falling" damage. Maybe that your body's movement is the cause of the damage could be argued for a Corpus bonus, too.
But, if you were to fall on metal/bone/wood spikes, wouldn't you apply its form bonus? So I see reasonable sticking to the surface's form.