http://wiki.guildwars2.com/wiki/Rune_of_the_Ranger
Test-case as following
Proffesion: Mesmer, un-traited ( 916 power ) using the PvP steady sword ( 121-121 )
Smacking the Target Golem: Light in hearth of the mist with Mind Slash, using 5/6 Rune of the ranger yields a consistent 30 damage.
Adding a 6th piece yields 32.
Summoning a phantasm/clone makes no difference for that matter.
Note, I did my testing counting only the initial swing, to avoid adding vulnerability to the equation.