[badger45]

I just tried it, and it is entirely possible to shoot smoke rounds through the smoke using X key. I don't see, where you experience problem. The ONLY problem I can see, is that when you use Z key for normal indirect fire, you see mouse pointer changed to crosshairs, if you are able to fire indirectly at that hex. But when you use X key, to fire smoke, your mouse pointer change to crosshairs only on the terrain, that is in your LOS. That however does not mean, that firing is impossible. Just try to click on the spot, that you can fire with Z key, and you will see, that you can use X key as well.

Hope that helps.
badger45