As for the length of the arc, there's a difference between how far a voltage can jump across an air gap that didn't already have an arc, and how far you can pull out an arc starting from a zero gap.
I also think this is capacitive coupling, there isn't usually all that much current in the cables, cos current makes power loss (I2R) where higher volts keeps power loss down. 20'/60' * 33kV = 11kV into a very high impedance, but a lot less into a human touching it. Don't go near!
