The breakdown of bromine to bromide by the UV in sunlight isn't affected much by pH at the ranges found in pools because most of the bromine is in the form of hypobromous acid and not hypobromite ion. This is different than chlorine that splits evenly between the two near a pH of 7.5 so the relationship is more affected by pH as a result.
Unfortunately, we don't have good numbers for the rate of bromine breakdown in sunlight but a rough analysis shows that it is slower than chlorine with no CYA but faster than chlorine when CYA is present. This is why a bromine pool tends to use more oxidizer to maintain a bromine level and to be somewhat more expensive to operate. It depends, though, on whether bromine tabs are used since they add DMH to the water and that may act somewhat like CYA in binding to bromine though perhaps no as strongly so only noticeable at higher levels.
