The best place to start is with 0's, this basically sets the attached objects to the exact vertex position of the vertex number you specified in the behavior panel. Then just tweak the values little by little to get the placement you are after.

Keep in mind if your object models origin is way off in med, then it will offset already that much. Also, don't forget to save and rebuild after you makes changes in the behavior panel.

Good Luck.

-raiden

"It doesn't matter if we win or lose, it's how we make the game."
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Links: 3DGS for Dummies