Yes, I miss DavidM too. He may have been a little headstrong at times, but he certainly brought a great deal of biomechanical knowledge and the ability to expound upon it to the table!
A small point: I would argue that it is not the hips, or the ilac crest, or any particular part of the body, that must be forward of the ankles to cause the soleus to engage. It is the center of mass that must be forward of the ankles. The CM may often be in the approximate vicinity of the iliac crests, but not always, and not necessarily. In a racing tuck, for example, the skier's hips are are way behind, but the boots, ankles, and lower legs, as well as the CM, can be appropriately aligned.
In my illustration, skiers A3, B1, and C3 show skiers in balance (CM slightly ahead of ankles), with hips well behind ankles. These skiers may or may not have enough ankle flex to trigger the soleus reaction, although even B1 might have enough--if he or she has very tight achilles tendons.