We have performed Monte Carlo simulations of the scintillation light transport between two adjacent 27.2 mm × 26.7 mm × 20 mm LYSO crystals, optically coupled together using Meltmount coupling medium with a refractive index of 1.7. Each crystal was read out by 4 Hamamatsu S11828- 3344M monolithic SiPM arrays from one crystal side. Event positioning reconstruction results show that this optical coupling technique can substantially reduce the edge-artifacts in these crystals. With realistic values for the multiplication noise of the SiPMs and electronic readout noise, we obtain intrinsic spatial resolutions of ∼3.1 mm FWHM at the center and ∼3.0 mm FWHM at 0.6 mm from the optical coupling edge of the 20 mm thick monolithic crystals. When reducing the number of readout channels by applying a 4 1 multiplexing ratio, a ∼4.1 and ∼4.3 mm FWHM resolution, respectively, at the center and 0.6 mm from the optical coupling edge was obtained. The simulations further show that a coincidence timing resolution of 350 ps FWHM can be obtained with this crystal geometry, with a 30% SiPM photon detection efficiency (PDE).