With a 40mm lens you could have lowered your shutter speed to 1/60 of a second and lightened the backround and also the depth of the shadow areas without changing anything else. Without varying the aperture and flashpower you can change the background by adjusting the shutter speed.
in other words: the apparent light from the flash stays the same when you change shutter speed, but the apparent light from ambient will change.
shots look good. i think you can see now that head shots, even 3/4 shots often don't require the best locations. once you go full body that's when you need to worry more about the background.

