Easley, O’Hara, and Basu (2019) show that transaction fees increase whenever the (coinbase) reward for mining a block goes down.

False. Easley, O’Hara and Basu find that transaction fees increase in case of queuing problems, not by reduction in coinbase rewards. This is because transaction fees get you priority to be on a block, so this price goes up when there’s a larger que.