tech arrow question

[dan ferguson]

Never have shot carbon arrows until yesterday, a friend gave me 2 GT 5575 to try. I don,t have any inserts other than the standard ones, I loaded up the shafts with enough weedeater line to get the arrow weight to 620 grns thats with a 125 grn point, tried to come close to the weight of the arrows i,m shooting. they have small fletching on them. they come off the bow tail high. Question I have does carbon need more weight up frount than wood or alum., or would it be because of the smaller dia I might need to move the nocking point down? The bow is a 68" 72#@28 fastflight string, 1/8 from center longbow.