Two things:

1) The CompacF mines at a minimum of 16 diff - I've coded it to not go lower.
The R909 miners at a minimum of 64 diff - I've coded to not go lower.
These values are already below what is needed.
People should expect pools to be pissed off at them if they tried to DDoS the pool with lower values.

2) All about worker difficulty: https://kano.is/index.php?k=workdiff