Not trying to callout an old post but just wanted to provide clarity on something I recently learned and that's that you can pile in if you're within 3" OR made a charge move. The second part doesn't come up often.
Core Rules 12.1 (emphasis mine):
"A unit is eligible to fight if it is within 3" of an enemy unit and it has not fought in that phase, or if it made a charge move in the same turn and it has not fought in that phase."
Simply making a charge allows you to make a pile in move with a unit even if the enemy unit it charged is no longer there. Since Chosen and Varanguard have loadouts with 2" reach weapons, you can pile in towards the nearest unit you're not in combat with and whack them with your 2" range weapons for an effective threat range of 5".