Performance comparison of the lower-dimensional three-feature model (left) and the higher-dimensional six-feature model (right) using the testing sample. The two subpanels show the fractional residual distributions; the solid blue line and the shaded regions represent the median and 1σ dispersion, respectively. The lower-dimensional model yields a relatively large scatter of 0.038 dex for the testing sample. In contrast, the higher-dimensional model shows no improved constraints compared to the fiducial model, with a scatter of 0.026 dex for the testing sample.