Are you overly concerned about the degree of absorption when you set the detection wavelength verifying the UV absorption of the component of interest?
Some substances greatly alter their absorption coefficients with a 2 to 3nm variation in the detection wavelength. Moreover, there are instrumental errors. In other words, however precisely you set the wavelength there must be small deviations. To avoid making the 2 to 3 nm deviation matter too much, it is important to choose a stable wavelength with little deviation of the absorption coefficient near the set wavelength rather than choose an unstable wavelength with high absorption.