  In this paper, we investigate the effect on energy resolution from changing
the angle and the position of incidence photon for a 5 $\times$ 5 crystal
matrix built with (25 $\times$ 25 $\times$ 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 $\sigma_{E}/E = 0.42 \% / \sqrt{E/GeV} \oplus
1.60 \%$ 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
$2^{\circ}$ on the 5 $\times$ 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.
