Ultras/Majors toughness affected by??? (Destiny)

by dogcow , Hiding from Bob, in the vent core., Wednesday, October 08, 2014, 15:40 (3942 days ago)

So, last night I was running around the moon patrol mode with 2 of my friends (which I typically do myself). I had the kill "10 Hive Ultra/Majors" bounty which I normally complete while running around Archers Line and periodically ducking through that domed building to the hive entrance where there are 2 yellow knights (level 6?). I normally two shot these guys with 1 sniper & 1 other round, but last night they took like 4-5 sniper rounds to put down. !?

Has anyone else seen this behavior? Does Destiny scale the toughness somehow? Is it based on party size? I didn't notice other foes being more difficult. Have the Hive wised up to my methods & posted some tougher guards on the door?

EDIT: minor details added.