I've no idea what causes the difference in krausen, but I've done three batches with S-04. Two had big ugly piles of krausen on the surface of the beer during fermenation, and one had nothing at all - so much so that I thought the yeast was dead.
Weird thing is, all batches turned out fine.
Bottle conditioning: Pliny the Elder clone; Tramp's Overcoat Barley Wine
Next up: Vanilla Porter