Similar to Figs. 6 and 7. We show the predicted size evolution of spiral galaxies, now illustrating the sensitivity to spiral arm properties. Stronger spiral arms (dashed lines) lead to much larger, more rapid structural changes than weaker arms (dotted lines). The three spiral symbols at the start of each trajectory are placed at the median redshift and size of the three arm-number subsamples in Figs. 6 and 7.