Mira was pinned down exactly as planned, unable to break from her cover because of the relentless chain gun fire while Alister was able to briskly evade the massive beam cannon. After that he transformed back into mech mode while in mid air and tried to fire into the barrel of the cannon while it was exposed. Still, that was a difficult target for Alister to hit while he was moving, and he only got a few shots off before he had to transform back and continue evasive action.