The flash shadows that you question are a matter of lighting ratios. If, for instance, you metered the "lit" flash output of a "split" lighting arrangement for proper exposure with a given film/camera/lens combination and then metered the proper exposure of the unlit portion of the persons face you would find that the lighting ratio would most probably exceed the exposure scale of any film available today. The answer to this problem is to provide fill lighting to those unlit areas. This can be accomplished by providing supplemental lighting through the use of additional strobes or by the use of reflectors to utilize the existing light in more suitable ratios.

The laws of sensitometry are incapable of being compromised. The film and printing paper will only hold so much exposure scale (contrast).