In this paper, we investigate the effect on energy resolution from changing the angle and the position of incidence photon for a 5 x 5 crystal matrix built with (25 x 25 x 200) mm(3) LYSO scintillating crystals. Those crystals have been proposed for the electromagnetic calorimeter of the Turkish Accelerator Center-Particle Factory (TAC-PF) detector. The energy resolution was obtained as sigma(E)/E = 0.42%/ root E/GeV circle plus 1.60% at the center of the matrix in the energy range of 50 MeV to 2 GeV. When we examined the dependence of the energy resolution on the incidence angle of the photon, resolution began to deteriorate at angles greater than 2 degrees on the 5 x 5 crystal matrix. Moreover, energy resolution at the corners of the central crystal was worse than at the center of the central crystal by a factor of 1.3 at 50 MeV and 1.1 at 2 GeV.