Blizzard made silent changes which you will not see in patch notes or their statement, this stuff was discovered in game files. There is atleast one thing in their patch notes even when its not direct info. Level of monsters is used for calculating quality of drops, in patch notes they are telling us that monsters in terror zones can have increased levels. Thats automaticly means increased higher quality drop chance. But i consider it as non significant as its too low increase. Most significant are treasure class upgrades which werent talked about at all from devs.
If ypu want to know more, i highly advise you to read my guide:
About your runs… Even increase chance doesnt mean good items are guaranteed. If that would be the case, everyone would have everything in few weeks.
Btw, for example terrorized diablo can drop stuff his normal version cant.