I know there are Improvements upon which one cannot place a spy.
One enemy got to the TirQuan (sp?) training trade good and built it before I could, getting the soldiering bonus.
I put a spy on the building and presumed that it negated the bonus, since the game engine let me put the spy on it. I also put spies on the Hyperion Shrinker and the Hyperion Logistics buildings.
A few turns later, I proceeded to invade four planets of that enemy on the same turn.
When I invaded the first planet, it said both the enemy and I had "Advantage 12."
The second planet was the one with the TirQuan bonus improvement. Again, both sides had "Advantage 12."
When I invaded the third planet - - after gaining the TirQuan bonus for myself -- it showed that I had "Advantage 14" and the enemy had "Advantage 10." Same for the fourth planet.
I can only conclude that the spy that I had had on the TirQuan bonus building had not been doing anything. Is it supposed to be that way? Or, is it a bug?
Can I then conclude that I am wasting the spies that I still have on the enemy shrinker and logistics buildings?