transmitter antenna down tilt question

We have a transmitter located on a water tower with a MTI Wireless Edge 12.5 dBi 120° 900 MHz antenna. Most of customers live well less than two miles from the AP. We have two problem customers that live 1.5 miles away and are roughly 25° from the center of the antennas azimuth of 270° . The beamwidth is 120° (typ) and beam (typ). Jay Fuller and I have discussed the possibility that the problem customers may be to close to the antenna and actually under the beam. Is there such thing as being to close to a sector antenna and would tilting the antenna down have any effect?

I have a POP with the same issue… I gave the sector a 2 degree down tilt and the SM linked up great…the only other issue is the longer shots suffered and had to drop power level on the closer units to uncover the AP… little management and all is good now… POP has 42 SMs on SE AP and 17 on the NW AP with great service… GOOD Luck!!!