My dwarf is a chopper so I am sure I can only chop two people if they are on the same side of me. The hapless, burning, soon-to-die enemy in the middle just hit my guys on opposite diagonals .
Pretty sure that's right, lord knows I've used chop like that before. He faces first target & attacks then faces second & attacks
A while back I changed Chop (and all multi-target attacks) to allow you to target all enemies regardless of facing.