Flux tube geometries considered in this work: (a) semicircular dip, (b) elliptical dip, and (c) sinusoidal dip. The solid line is the flux tube with the smallest radius of curvature. The dashed line is a case with a radius of curvature intermediate between the minimum and the maximum. In both Models 1 and 2, the end points of the flux-tube components change in order to keep the total length of the field line constant.