My poles go a few inches below my waist. (I am 6ft). I like short poles cause landing on them or getting impaled with one when you crash is not fun. I also dont use pole straps so I can eject if I want.
Mogul skiers (like Tanner when he was younger) use short poles as well - that's where the shorter poles originally came from - when the bump guys started skiing park they probably just kept their short poles because you don't need/want longer poles for park.