Board Thread:The Quarters - Q & A/@comment-136.50.4.4-20190129002241/@comment-25085701-20190129002945

Yep! When you have a Perfect Day (all Dailies completed for that day), you get a stat bonus based on your level (1/2 your level) as a bonus. On the days you have that bonus, you will hit harder and have a higher chance for critical hits (due to higher Strength), so there's your difference right there.

If you're in a party, and someone else has cast one of the buff spells, that is also a factor.