Non-Orthogonal Multiple Access (NOMA) schemes superpose multiple users in the power domain. It is commonly assumed that the achieved throughput in a downlink NOMA system increases with the channel gain difference between paired users. This paper investigates the accuracy of this claim when different intra-subband power allocation techniques are studied. Moreover, the Proportional Fairness (PF) scheduler is used as a resource allocation mechanism to highlight the importance of the choice of user pairing and of the intra-subband power allocation scheme. Results show that the achieved throughput does not always evolve in the same direction as the channel gain difference between paired users, owing to the choice of the intra-subband power allocation technique. In addition, it was found that the PF scheduler is not fully adapted to NOMA.