All good post so far. Getting BH's and fieldpoints together can be a bugger. Most of it is attributed to either improper spine, or fletch contact. C903 makes a good point. You added weight to the rear of the arrow, which in turn weakened your spine a bit. Also, you changed the FOC of your setup. Most times, a little move of the rest can tune them up fairly easily.

Basically, you changed the charictoristic of the arrow in flight by adding weight. You should be able to tune that out by moving the rest.