Originally Posted by Mrclasen
Although this seems like the best answer to me I am just curious as to why would their be a different density of wort if everything was at a rolling boil for 90 minutes and then went straight through the plate chiller and into the carboys for fermentation in less than 15 minutes. To me it seems like the boil would have kept everything pretty well mixed and the short period of time wouldnt have allowed for their to wort to settle that much and create that much difference in density between the two.
With the plate chiller I wouldn't think there would be much difference, though there could be a little. At a club meeting I recently helped someone with a similar issue but they pitched the same yeast in each. After walking through everything this is what I came up with. They use an immersion chiller though and just let it sit while cleaning up other stuff.
I'd guess different levels of flocculation between the strains. Maybe different total volumes in each that caused yeast to reproduce more, or maybe even different reproduction rates of the yeast.
I'd be interested to see how this turns out. I'd guess in the end after the yeast drops they will be pretty similar