We need more blocks and more luck

It seems that BTC per THs is reduced from 0.00035732 on April 26 to 0.00021599 today. But the number of blocks is 2 on average. I am not sure whether it's entirely due to difficulty or not.
I would think it would be due to the hashing of the pool as a whole going up quiet a bit during that time period. Almost 30Ph during that period. Rewards being spread around to more workers.