The Purple engrams you get from any activities (Non-Powerful gear) are your maximum ilvl minus 10. So the only way to increase the engram level is to extend your maximum ilvl by getting Powerful gear from Milestones or Exotic engrams
My drops have been 318 , and last night I got 3 Legendary , and 1 Exotic in one heroic event. Oh how the tide flows in , and out! Patients is the quality of strong men in times of war. Optimist prevail