Most of the time when we get this issue we discover that it can be one of a few things:
Non-Amplified Indoor Antennas: 10 mile VHF range.
Amplified Indoor Antennas: 20 mile VHF range.
Roof/Attic Mount Antennas: 45 mile Vhf range.
Translator Towers: If the tower that is transmitting your signals is a translator tower (one that receives signals from one tower then sends the signal along) it tends to transmit at a low signal strength. Some towers will also transmit at a lower power level as a cost saving method. Unfortunately there is little that can be done to improve reception if this is the issue.
Transmitter Blockage: Transmitters can actually "line up" one in front of the other geographically and the signal that the further transmitter is sending can be blocked or the signals reflected by the closer tower. You can try re-positioning the antenna however it may be difficult to improve reception when this occurs.