Flanking

Chk Chk and Dae are flanking the tashtari alpha because they can draw a line to each other that passes through opposite sides of the tashtari's space. The tashtari is off-guard to them, taking a –2 circumstance penalty to its AC. Obozaya isn't flanking the tashtari alpha because she can't draw a line to Chk Chk or Dae that passes through opposite sides of its space, and the tashtari alpha isn't in Navasi's reach. The tashtari and the tashtari alpha flank Navasi since she's within reach for both, and they can draw a line between them that passes through opposite sides of her space. If the tashtari alpha didn't have 10 feet of reach, the two creatures wouldn't flank her.