  We resolve the long-standing open question of how the transport model AMPT
manages to generate sufficiently high elliptic flow (v2) in A+A reactions with
only few-millibarn 2->2 partonic cross sections - in apparent contradiction
with an early study by Molnar and Gyulassy. Through detailed comparisons with
the covariant Molnar's Parton Cascade (MPC), we pinpoint which features of
initial conditions, interactions, and dynamics encoded in the partonic stage of
AMPT allow it to circumvent the "opacity puzzle" at RHIC.
