Right now, moving a soldier into a vehicle will fill the first free position. Sometimes it is more desirable though to be able to pick exactly which position a unit should occupy.
Feature Request: Implement one of these two options:
Option 1: When moving a unit over a vehicle, show extra icons for each position. Releasing the unit just over the vehicle will mimic the current behavior. Dropping him onto an icon will move to the specific slot
Option 2: Drop the unit into the seat/position closes to the point where the mouse pointer is released.