That would be a mechanic of the game, HotKeyNet doesn't have a way to intuitively track that since it doesn't have any way of "reading" the game, which is true for all multiboxing programs. This is why there are very few people even attempting to multibox Tera. You will have to manually position the mouse on the slave. You can try using ActiveWindowTracking to automatically bring the windows into the foreground when you need to position on the slave, but there's not going to be anything simple about managing slave targeting.