https://mattepaint.com/academy/tutorial/realistic-reflections/

This video takes a different approach, here we decided to record the full process or exploration and troubleshooting so you can gain an insight to how a professional matte painter problem solves a visual issue in the artwork.  The video covers 2 main techniques for creating reflections: the first is the more typical approach, flipping a layer and distorting, masking and grading the image to look like a reflection that matches the environment.  The second half looks at a special technique using a distortion map in photoshop, this will make your reflections look far more realistic, but it requires a bit of trial and error.