Hint 1: Stack the auras together!
Hint 2: Three archers and a mage fit just right on the buff beams at each choke point.
Hint 3: I like to place a few extra archers here because a) I have extra MU and b) this is a high-stress choke.
Hint 4: Four archer minions at each crystal is more than enough to protect from fliers.
Hint 5: This buff beam may need to go up/down the stairs rather than across to get everything, depending on how your auras and traps are positioned.