Had an opportunity to test that today. Entered the ogre keep in Alvar. In turn based mode. Right from start i can hit the mercenaries (human swordsmans) with two of my rightmost characters (4 people in party) but two leftmost characters would hit the wall instead. Provided the possibility to swap the members around, i would be able to shoot them with all four party members.
This is 100% confirmed and yes here order does matter. It can happen in any confined space.
Also, when i started the game (necromancers only) i first leveled mine to 5 then took the necromancer from the tavern. When they travelled along, i dont know why, but my hired necromancer was taking almost all the ranged hits (especially lizardmen friendly fire...) and most melee hits.
This could be (speculation but it looks like this) because the attack hits the portrait 3-5 but no person there, so it looks for the closest portrait (2) and hits him. Maybe it was just monster preference i dont know (i was fighting pirates, and monsters from abandoned temple)
