Top panel: variation of the phase shift with L for the azimuthal orders m = 1 (solid line) and m = 2 (dashed line). Bottom panel: variation of the phase shift with m at L = 2364. In both panels, asterisks correspond to the simulation with a flux tube with a 170 km radius, diamonds to the flux tube with a 370 km radius, and crosses to the flux tube with a 560 km radius. The dashed line in the bottom panel corresponds to the 560 km radius flux tube at L = 1765.