Problems with GUI and Resolutions. (C#)

I'm adding the HUD/GUI to my game, and I'm having problems making the health bars stay with the rest of the game's HUD, it changes place depending on resolution. The scaling works fine, perfect even, but as far as position goes, it's all over the place.

[Here's what it's meant to look like.][1]

[Here's what it looks like when the resolution is too big][2]

[Here's what it looks like when the resolution is too small][3]

Not sure if it makes a difference (I hope not!), but the Main HUD and the Health bar are using separate scripts, but are drawn from the same one, the main HUD script, I'm getting the Bars position, scale, and how it changes size (e.g. if health or armour goes up or down, or some other value has changed), the main script references this when it draws the texture.

Here's my code:

Main HUD:

             foreach (GUIBarScript bar in GUIBars)
             {
                 if (bar.stayWithMainHUD)
                 {
                     if (bar.texture)
                     {
                         GUI.DrawTextureWithTexCoords(new Rect(positionAndScale.x + bar.positionRect.x, positionAndScale.y + bar.positionRect.y, bar.positionRect.width, bar.positionRect.y),
                             bar.texture, bar.sourceRect, bar.transparent);
                     }
                 }
                 else
                 {
                     if (bar.texture)
                     {
                         GUI.DrawTextureWithTexCoords(bar.positionRect, bar.texture, bar.sourceRect, bar.transparent);
                     }
                 }
             }
         if (texture)
         {
             Rect positionRect = new Rect(positionAndScale.x, positionAndScale.y, positionAndScale.width * Screen.width, positionAndScale.height * Screen.height);
             GUI.DrawTexture(positionRect, texture, ScaleMode.StretchToFill, isTransparent);
         }

Health Bar:

             sourceRectX = (float)masterScript.health / (float)masterScript.maxHealth;
             positionRect = new Rect(positionAndScale.x, positionAndScale.y, sourceRectX * (positionAndScale.width * Screen.width), positionAndScale.height * Screen.height);
             sourceRect = new Rect(0,0, sourceRectX, 1);

What's causing the problem? [1]: http://i123.photobucket.com/albums/o305/Dinoco07/Problem_zps2da6fee6.png [2]: http://i123.photobucket.com/albums/o305/Dinoco07/Problem2_zpse7e089bf.png [3]: http://i123.photobucket.com/albums/o305/Dinoco07/Problem3_zpsc7cca4ca.png