Should you be overly concerned about the degree of absorption when you set the detection wavelength as the optimum for UV absorption of the component of interest?
The absorption coefficients of some substances changes greatly with a 2 to 3nm variation in the detection wavelength. In addition, the instrumental errors can indicate a wavelength different to that actually being used for detection. In other words, however precisely you set the wavelength there may be small deviations. To avoid making such deviations having a significant effect on the results observed, it is important to choose a stable wavelength which gives little or no deviation of the absorption coefficient near the chosen wavelength rather than choose wavelength with high absorption which gives unstable results.