What was said below - it's about the fullness. If the skirt's going to be tighter, then it needs a slit/kick pleat somewhere or it needs to end before it interrupts the ability of the thigh to move forward freely. Amy's has all three - there's a bit of flare there, it ends fairly high but not abnormally so - hell Jo would think she was wearing a maxi skirt! - and I'm pretty sure I've seen a slit.

(Speaking as someone who's pelted all over rennfaires with more than one ankle-length skirt on at a time, length doesn't slow you down at all.)