RE: Muzzy 90gr 4 blade grouped 4in below points 2day??
I had the same trouble. Got very frustrated trying to tune them in with the bow. I ended up screwing with my tiller and still couldn't fix the low impact. Sent the bow to the shop had the tiller re-set even and a Muzzy ZE rest installed in place of my biscuit and started over. Had the bow tuned in 15-20 minutes and it is shooting better than ever.
One suggestion with your issue. Some more info would help but what arrows/bow/spine/fletch are you shooting? A larger fletch and helical may help. I believe my arrows may have been flying nock high with the 90's. I was using small vanes and they didn't have the drag to stabilize the arrow enough, thus causing the nose dive. Just a theory though.