Mixing Non-Diegetic sound with Diegetic sound

When I have used dialogue throughout my opening, I have left the non-diegetic sound running quietly in the background to leave it to build the tension. At the end of my two minutes is the only time I have lowered the diegetic sound for the non-diegetic sound to take over. I have chosen to do this to add suspense to the car pulling away as the audience has seen that the driver gets kidnapped but they do not know why or how, this adds to the tension I want to enforce with the music.

On Final Cut, I have lowered the diegetic sound, and enhanced the non diegetic sound to leave the two minutes opening on a high suspense level. This is a screen print of how I have done it.