The famous dura graffitto of a cat shows his armour to fall to knee length.
The example found in dura barely covers the chest, with much of the lower torso exposed .
Is there any evidence for the longer armour?
I've got figures for both, and seen figures of the front armour cats of later eras that do dip low.
The Sasanian spahbed seals show barding that's roughly knee-length - see http://www.sasanika.org/wp-content/uploads/e-sasanika7-Safdari-Daryaee.pdf, or http://www.artemissionblog.com/wp-content/gallery-bank/gallery-uploads/o_19q3ooa3fmt1ausah1pgl1oef1t.jpg for a quick pic. The Tang-i-Sarvak horseman's bard is almost knee-length - http://www.iranicaonline.org/uploads/files/Tang-e_sarvak_plate_iii.jpg
Otherwise, I believe the internet is full of pictures of cats, some no doubt in skirts.