My OTA numbers are always bouncing around and I haven't been able to determine what is considered a good/lockable number. I'm in the DC area though so your numbers may be more steady. Have you looked in the thread for your area if there is one?
I was getting 0 locals and had a signal of around 19. It fluctuated, but it stuck around 19-20 most of the time. Sean was able to get me re-mapped to closer locals and now I get CBS and NBC, but my signal strength is still hovering in the 19-20 range.
My installer told me that anything over 50 was considered a success for OTA.