you would have been just better off going with the force field generator asset attached to the pad. All units then receive a 4+ invulnerable save and some counter becomes the generator on the pad. Therefore, you don't lose the objective and the units still benifit.
Funny enough if you just used it as the planetstrike landing pad with the added caveat that it could not be blowed up, you would have your 5+ invuln and no arguing would take place.
Actually, it was defined last week as having a wall around the landing pad, in addition to the void shield. The wall provided a 4+ invuln, but it had to be lowered in order to land the flyer.
In the haste to get the flyer on the ground before getting hit by ack ack, the wall wasn't taken down before the flyer model was placed on the pad. I'm also not sure, if the center of the orbital bombardment circles are all inside the wall, if the wall should have provided any cover for stuff inside the circle of the wall. It seemed prudent not to open these discussions, however. I just played on. I doubt we'll see moving walls again, but if anyone has opinions on orbital bombardments centered on skyshields, it might be nice. That could certainly happen again.
I'd recommend keeping it simple in the future. Simple, or more carefully defined. Simple would be simpler.