Oxalis adenophylla

My Oxalis was flourishing in recent months.  It is in full sun, planted at the edge of my alpine bed, and planted up against the side of a boulder.  In recent weeks it began to wilt and now looks awful.  Over the past year or so, the bulb/crown had become quite raised, so I covered it a bit with compost last week.  Could that be the problem, should the crown be exposed?  We're having a heatwave, and I think it isn't getting enough moisture, possibly aggravated by heat stored in the boulder.  What's most risky, over or under watering it?