A lot of times I feel like the city backdrop needs to fit the scene, you can always give miniatures and forced perspective a shot, although forced perspective is a lot harder to achieve using the wide angle lens on a webcam.

You can always use a miniture and then cut to a more close up shot to achieve a scene of scale in your films like I did here:

(although it would be a gross lie to say that the next set I cut to in that film was 'small' by any stretch) Also a lot of scale can be achieved with sound design, a lot of the scale in The Letter is achieved with sound design and hiding the scale limitations with close ups. Never underestimate what adding sounds for stuff that occurs off screen can do for your films sense of scale.