Wavelength–dependent encircled–flux fractions for different aperture radii, shown relative to a large reference aperture of 1$\stackrel{″}{.}$0. The legend reports the corresponding chromatic flux losses as defined in the main text. A 7–pixel radius achieves percent-level chromatic flux loss while avoiding the increased background and extended–emission contamination present in larger apertures. The spline function fitted to the 7–pixel curve is shown as a red dashed line. The blue and red bands correspond to the regions we compute the chromatic flux losses from: (2.9–3.5 μm) and (4.5–5.1 μm.)