Getting Image world height

I'm currently trying to get the world height of an image that spans the width of the screen with a relatively small height. Here's how I currently calculate this height:

 bottomBarHeight = (Camera.main.ScreenToWorldPoint(new Vector2(0, bottomBar.rectTransform.rect.height)) - Camera.main.ScreenToWorldPoint(new Vector2(0, 0))).y;

In the unity emulator this returns a height of roughly 7. The camera height is about 10 and the actual height of the bar is probably around 2. When I run this on my real device it's almost accurate but still not correct, with the calculated hight coming out to be slightly smaller than expected.

I'm not sure what I am doing wrong here and would appreciate any advice!