The other way - with -40 they might start closer than with -20. When i rmember correctly the value is applied as follows: Base minimum distance - how many plots must be between two starting plots - is somewhere in xml. The base is assumed to be 100%, while the value from the method modifies the % value. So at -20 starting plots might be as close as 80% of the base value. At -40 this would be 60%.