And if you cannot do a random location spawn for the P-3 then maybe set up 10 different spawning locations (some closer, some far away) and give each P-3 a 10% chance to spawn. This way some times we get 3 of them, sometime zero. I love randomness.

Fun. It might be even more fun if you have a P-3 spawn somewhere random on the map at the start to make those Echo II's sweat after first launch. They do radiate in the game, don't they?