I think it's the Trigonometry I don't get, having not applied it in a long time and so have lost it. I messed with your example and put in a few things.
The bullet, like the player, would be something that corresponds with the invisible layer. All "real" objects are on Layer 1, while all "overlay" objects appear on Layer 2. Layer 1 will be hidden, so no one will see that, while having that is useful for working with 360 degrees without having to put in angular alterations (but consequently more objects will be needed).
And yes, the height value is what I'm trying to work with. I named it "Altitude." I could make it so that it can calculate the distance and speed and then raise or lower depending on that, but at extreme heights difference with small X/Y distances, this gets to be a problem.