Recently, underwater visible light communications (UVLC) have attracted much attention. However, the application of UVLC has been limited to the deep ocean. In order to realize the UVLC in shallow water, UVLC with the maximal-ratio combining scheme applied to angle diversity receiver was proposed and, in particular, the optimization of PD placement has been studied. However, as the field of view (FOV) of each PD was fixed at 90 degrees. Therefore, this paper investigates the optimal FOV of PDs that maximize the average SNR of a square communication area of r^2 centered at the initial position of the receiver.