In multiplayer game, how are the numbers of invaders to be given to your opponent determined through the combo?

1. Shoot down an enemy invader or form a particular Feature
2. The enemy invader is added to the "Invader stock" box (Attack box)
3. Shoot down a UFO
4. After shooting down a UFO, the enemy invaders that are showing in the invader stock box will be sent over to your opponent

You can stock up to 12 enemy invaders at a time in the invader stock box. There are five different colored UFOs. The types of invaders that are sent over to your opponent is determined by which UFO you shoot down (meaning, not all 12 invaders are sent over to the opponent all at once).