In case you just added the -dx command and went ingame, you need to undock from a station to see the changes. When you first go ingame, the upper hud part, and some parts of the lower hud are off the screen. But when you undock, these things fix themselves.
And if you mean how the hud isnt on the edges of the screen in widescreen mod, thats just a bug that you have to deal with.
