Well... I may have answered my own question. Today I had large yeast families just barely visible rising from the ashes up about 60% to the surface before falling back. Still lots of clingers to the side of the carboy almmost to the top - which in the past seems to coincide with active yeasties. So guess it just wasn't as vigorous for as long as I'd expected for this relatively big beer. I'll forget about it til the weekend...