[Lemmy]

i noticed that too, the missile must always reach the far end of the planet to hit.
I encountered this in tactical combat, ships where just in range too hit one corner of the planet, so i fired, but once the missiles where over the planet, they did no damage, then i moved one sqaure closer to the planet, and fired again, this time the missiles went to the far end of the planet and exploded.

you could see this as a feature, your missile also must have enough fuel to go through the atmosphere.