Worked on cover a little more this evening. Decided to see how adding depth by putting in shadows from the sunrise would effect the composition.
After adding shade to the foreground images, I tried continuing the effect by adding shadows to the upper section of clouds and to the figures in the background (to follow realism of light/shade), but the picture started to look too segmented and messy. What I mean is, it just started to take away the crispness and 'punch' by all the shadowy complexities.
So instead of adding a shadow above each cloud, I simply faded the outline of each cloud to give the suggestion that the top of the cloud is darker than the bottoms. And instead of adding small complicated shadows to each background person, I simply increased the opacity of the grey on them as a flat colour.
Getting the right effect to convey doesn't always mean being literal.