Im no tunning wizz, but I just finished tuning two bows this morning, and after MANY fits, it came down to brace hight. I did everything under the sun, and I had the bow set at the bowyers recommended brace. I couldnt get my bare shafts to come anywhere close no matter how high or low I moved the nock, no matter how many times I changed the tip weight.
I FINALY started playing with the brace, and things came together. I went between 1/4 to 1/2" above the recommended height and I started grouping nicely.
Its worth a try....