Without thorough research with devices, you cannot differ the real sun and its reflection.
Please produce the thorough research you have done that allows you to differ the reflection from the real sun, as you claim.
If you cannot, how do you know it's a reflection?
Everything takes time... I can't promise it will be soon comprehensively presented.
Why reflection? Because the dome is real, more than just a belief. Various experiments have been performed : helium balloon, rocket, photo etc.
In the video, the actual sun looks bigger than its reflection (which people think it's the real sun AKA midnight)
Because the dome which reflects the sun ray is more distant than the actual sun itself. So the sun reflection looks a bit smaller than the actual sun.