Non-orthogonal multiple access (NOMA) scheme enables serving users with the same resource block i.e. frequency or time by multiplexing the signal of the users. Intelligent reflecting surfaces (IRS) or reconfigurable intelligent surfaces (RIS) is a potential approach for increasing transmission efficiency by modifying signal propagation by tweaking typically passive reflective components. IRS reconfigures the wireless network in this manner to improve system performance. The research considered an IRS-assisted downlink NOMA system. This work modified the reference model by adopting an IRS-specific frequency-distance-dependent path loss model for IRS-NOMA downlink received power and signal-to-interference plus noise ratio (SINR) measurement instead of a typical or conventional distance-dependant path loss model. The incorporation of an IRS-specific path loss model provides a more convenient and better measurement compared to the conventional path loss model. Furthermore, this work figures out an improvement scope in the reference model.