I have 80 GH myself solo mining.  There are a lot of people like me that have say 20-30 GPUs so a few others like myself can make the difference....also you need to understand that its not actually 1.67 TH.  Its actually closer to 800 GH.  What happens is as (by chance and in conjunction with the other algos difficulty levels) the difficulty adjust reports higher hash as if by chance several blocks are found with one algo in a row...track it over a longer time period and you will see the average is no where near 1.6, thats a high number.

There is a complicated reason for oscillation which I wont get into as it requires an understanding of the difficulty adjustment algo and information delays(remember we only "guess" the actual hash-rate based on the time in between blocks being found, its retroactive with more recent block inter-arrival times being weighted more heavily)...but the bottom line is Unitus does a very good job actually managing the difficulty with imperfect information about actual hash rate.  (side note: when people switch from one algo to another rapidly a consequence is that the range of difficulty/reported hash-rate swings become much larger, this is a major difficulty to manage with a coin that has 5 algos, I am really impressed that the variance seems to be within a factor of 2 of the real hash-rate...for example NEOs couldn't solve this problem).

If this made no sense to you I can further elaborate,