I don't know about the A321, but the A320s and E190s have the same plan except the E190s don't have group E. I have this document for the A320 that specifically says DO NOT DISTRIBUTE, so I can't reveal exactly where the cutoff is, (so pax will have to figure it out for themselves through deduction). What I can say is that the cutoff is at a particular row, and that row is farther forward than you might think. Of course, this is subject to change, as JetBlue may tweak the location of the "demarcation row" in the future if they think they can make boarding more efficient.