If I remember correctly NPCs don't move when you are near them. Guard from Rhoneis helped me to kill orc commander and after it have been waiting for something near 20 sec.
NPCs often block me in entrance in main office of wisards' guild.
Walking NPCs stop moving when you are near and continue after you leave them, like mercenary in Icemist near guild. Staying NPCs, like guards, maybe, just want to return on their position, but you block them as they block you.