I've been playing multiplayer for a while now, and the reaction fire seems to be really random. Sometimes the enemy reacts after I've given my soldier command to fire but before I get the shot off the barrel, and sometimes I can valse in front of a crouching enemy and he doesn't do anything. Worst cases are when I have soldier in enemy's line of sight and move another soldier on the other side of the map. Suddenly the enemy reacts shooting the first soldier though he didn't do anything.
I think that the reaction fire system should be more predictable in multiplayer mode. Now it isn't useful as any kind of tool. You can't count on it to work so you can't use it, but on the other hand you can't count on it not working. I tried to browse the wiki and forum for more insight on how it should work, but didn't find any specifics. If the reaction system is still in progress, is there anywhere I can find info about how it is currently working and what is to come.