Pleated skirts are definitely different from pleated pants, which tuck back in under the belly and emphasize it. In the skirt, the curve of the belly is masked by the flare of the skirt, which continues to widen as it goes down, implying a sort of hourglass shape.Dirndls are quite different: their fullness starts right at the waistband, and doesn't flare as much further down, so the belly can be emphasized or the waist thickened.
Can you tell I love pleated skirts?
I can't comment on the length (I am 5'7"). Except to say that where the skirt stops on you is a matter of proportion more than height. I am long waisted, so a knee-length skirt can look very awkward if the top is tucked in or belted, because it chops me right in half, or worse, the top half is longer! I do better with tucked top and midi length skirt, or above-knee skirt with a long, untucked top almost tunic length. And with an above-knee pleated skirt, there isn't really enough length to get the full effect of the flared shape, especially when the waist is covered by an untucked top; pencil or really full (skater) skirts are more flattering at that length I think.