Steve hit the nail square on the head. There’s one part of his response that bears repeating.
“Now to your first question- Bows that have a deeper shelf are said to be easier to tune. Meaning a wider range of arrow spine will fly well out of them.”
That explains why (until you get to very near dead center) the closer to centershot your bow, the more forgiving it shoots. Being less sensitive to spine means it’s less sensitive to inconsistencies in shooting factors that affect dynamic spine—draw length, release, bow torque and such. One of the main reasons for tuning our bows (in addition to eliminating broadhead wind planing and increasing penetration due to straight flight) is to make them more forgiving to shoot.
This is why I rarely, if ever, suggest people build out their strike plates to tune a weak arrow. To me, it seems counterintuitive to tune a bow in an attempt to increase forgiveness by making a change that will reduce that forgiveness—one step forward, one step back. As a side note, the Easton Tuning Guide lists several ways to correct for weak arrow spine, none of which include building out the strike plate (decreasing centershot).
