I found some extra features hidden on an 'Advanced' options page of my Samsung ML-1520. One of them was a toggle between 'Normal' and 'Dark', it seems to make it lay down more toner
Will see what the result are soon.. still homing in on a repeatable process with understandable reasons why it might of gone wrong.
So far I treat the whole board with the same loving care and attention, yet one bit of toner decides to unstick, while the rest is glued to the copper solidly.