Ok, I'm thoroughly confused now. I used quick battle, selected the airbus, desert, scout, mercenaries, min darkness. I took some F10 snapshots and couldn't find any obvious hole through the back door of the airbus, but that doesn't mean its not there. So I went in debug mode, used ctrl-w to stick the merc commando inside the airbus right next to the back door and stuck 4 gals outside near the back door. None of the gals could see him (at least no flashing numbered red square nor green square for that matter) but all were able to fire at him without force fire with straight trajectory weapons (rifles shotguns). No shots penetrated the door. Moved merc one cell away from door still inside airbus. Was unable to fire at him and the door was momentarily highlighted as blocking terrain.
Moved merc back next to door still inside airbus. Tried throwing objects at him (hadn't bothered to arm gals with grenades, so used lightweight items like ammo). Got the "unable to throw here" message without seeing any highlighted blocking terrain. Kept trying (I have confirm fire on so I have to click twice) with the same gal in the same spot and after 5-6 tries the object was thrown and landed in front of the door on the outside of the airbus. It seems to matter where the yellow mouse pointer is inside the red wireframe box when the throw occurs. Near the left side, near middle vertically on the second click when the yellow circular targetting reticule is displayed seems to allow the throw to occur. This seems to be a bug since it shouldn't matter where I click so long as the same cell is selected. As before, moved the merc one cell away from the door still inside the airbus, and was not able to throw at him no matter where I clicked. However, each time the door was momentarily highlighted as blocking terrain.
No other mods installed x-piratez version 0.99J8, extended version 5.1 (v2018-10-14) if anyone cares at this point.