Norm,
I do not know the setting you are using on your camera but I can assure you that unless use of the flash impacts on the shutter speed and aperture selection, then use flash will have no impact on these distant images. My Metz which is fairly powerful, with a guide no of 45, will reach 30 ft at f4 at ISO100.
Although your eye can see the light from even a small flash at quite a distance it is insufficient light to record on an image. The rule for flash is that as distance doubles light reflected from the subject falls to a quarter. ( Inverse square law ). You can see that for yourself if you do a night time test with the camera set in flash mode. Take a series of pics at 6ft, 12ft, 24ft and 48ft. By the time you reach 48ft almost no light will be recorded unless you have a powerful flashgun.
Don
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