I just finished playing in the Imperious Task Force, which ended abruptly due to a lack of healing. However, in the grand scheme of things it was fruitful. In the second mission, the one with the Shadow Cyst Crystals, I realized a way to avoid the ambushes and finish the mission in a prompt manner. For those of you who are interested, here it is:
First sweep through the entire map, kill everything BUT the crystals. (The destruction of the crystals causes an ambush by an Elite Boss and company). Once you have cleared the mission, minus the crystals, destroy the two closest crystals together, and then place one person on each crystal. Keep the team updated to the status of the crystals health bar, and once they are all incredibly close to death, have each member destroy their crystal. By doing this in unison, the team avoids the ambushes with the Exit button.
Mind you, in my case this was done out of desperation, but worked magnificently.
(If this tactic has already been stated, my apologies, but I felt it necessary to share)