You can see how pretty close to each other they were and interpret for yourself how much randomness there is.

UPDATE 3. april 2013.
I had to make some more dry planks, so this is an even bigger update. This time spacing was uniform (5 whole tiles between bounding boxes).
All piles were outside claim, on a 3X3 flattened ground (not perfectly flat) with just one paved tile in the center.
Cheers
