I am wondering if it is possible to reflect object that are behind the main camera for better and more realistic reflections
Screen Space Reflections (SSR) work with the color/depth/etc. buffers of the current render to decide what should be reflected. This is an alternative to more-realistic reflections handled by re-rendering your scene with a second camera (or more) with an oblique frustum/slanted clip planes.
In short, anything you can’t already see on screen won’t be reflected using this method.
As an added note, this is also why various developments of Screen Space Reflections tend to forcibly fade out near the edges of the screen (scaled based on the reflection angle), even if the viewing angle would have otherwise been eligible for a reflection, to smooth the transition between reflection and not a little more.