I had this problem once on a bow that was not cut to center, slightly outside of center. Every arrow (ranging from carbon express heritage 75's all the way to 350's) that I shot out of this bow looked weak when bareshafting it. Due to this I built out the strike, still no change.
I finally had someone help me out that had far more knowledge than I had. Come to find out, I was getting a false indication. I took off the strike plate that I had built out, replaced it with the thinnest one that I could find, and added more point weight to the heritage 75's. I was finally able to get it tuned.