i tried scaling down my impalements. sometimes impaling someone on a 30ft long pike is very difficult, especially if we lack all the ropes pulleys and manpower we require. So in a pinch i impale someone on shorter pikes. The shortest one i've used is about 8ft but that's not a very good impalement. I'd go for 16ft poles if that is what is handily available in lumber supply mills. You might try finding out who supplies your local utility company with their utility poles and then retrofit / taper them for the purpose of impalement.