There was a succinct rules clarification I found useful,
"When evading you roll to see how many moves the evading unit can make and then it moves as far as possible. If the evade move will not allow them to clear an intervening unit, then it stops its move immediately in front of the intervening unit because that is as far as it could possibly move.
[Horse archers] could not countercharge Roman [cavalry] because it is a unit in Open Order and the Roman cavalry are a formed unit (see Units Not Allowed To Charge on page 55)."
Also a cryptic tease from Craig Woodfield regarding some HC skirmish rules his group has put together that may see print!