Evolution of the disk radius of π Aquarii derived from Hα emission line measurements using Huang’s law. The disk radius (blue points with error bars) shows significant growth across five epochs, increasing from 4.9 to 64.9 R_⊙. The Roche lobe radius (red shaded region, 124–131 R_⊙) and orbital separation (green dashed line) indicate that the disk remains well within the Roche lobe and is not truncated by the companion star. Errors represent uncertainties in the Huang radius.