How to scale orthographic camera to match screen space overlay canvas

Hello, I am rendering some UI elements in a canvas set to screen space overlay mode. For various reasons I won't get into the mode needs to remain screen space overlay. When the UI elements move, they render a trail using a trail renderer component. This component creates a mesh, so I need to render it via a camera.

So my question is how can I match the orthographic camera to the screen space overlay canvas? I've tried adjusting the viewport settings and size setting but on device it doesn't match up.

Any tips would be appreciated. Thanks!