How To Position Camera ViewPort Rect (Y) At The Bottom Of An Image & Size ViewPort Rect (H) With The Top Of The Image?

Hello, I was wondering how can I position/size my camera viewport rect with a image height Rect, starting from positioning viewport rect (Y) with the bottom of the image & sizing viewport rect (H) to the top of the image. I've finished a project for mobile & I do not want to use the full screen, instead I want the same height & centered for the viewport rect on every device so that way all gameobjects/UI looks & fits the same. is there a way I can do this? (The image canvas is set to 800 by 600, Camera projection is Orthographic.)