Drawing a targeting reticule

I want to draw a reticule to the centre of the screen. I'm using this code inside OnGUI():

GUI.DrawTexture(new Rect((Screen.height/2)-5, (Screen.width/2)-5, (Screen.height/2)+5, (Screen.width/2)+5), texReticule1, ScaleMode.ScaleToFit, true, 1.0F);

(The image is 10x10 pixels, and is supposed to stay that way on screen).

It's not drawing to the centre. Instead, I can only see it if the screen is not set to a widescreen mode. It appears half off the bottom of the screen, half on (in 4:3 ratio). It's so large that, if it was all on the screen, it would take up a full quarter of it.

Not looking at the docs right now, but I think the arguments to the Rect constructor are x, y, width, and height, not the bounds of the rect.