FWIW - I recently pitched a packet of yeast into some chilled and well shaken wort (about a liter) and then an hour or so later, I poured it into the full batch. I observed no difference in any aspect of fermentation between that and sprinkling on the surface of the full batch. I don't know why I even thought to try this, but I did. So, from now on (and as I have done routinely for the last 3 or more years) I will just sprinkle on the surface of the full batch of chilled wort and let it do its thing. Thanks for the definitive update.