I suspect this isn't high on anyones list but ...
Assuming small shields are buckler style (small and round) and as shields get larger they get more unwieldy and less aerodynamic shouldn't the damage from using a small shield actually get better damage marks than larger shields. An eternium small shield would effectively be a discus style weapon so an eternium one could perhaps give 2d6 or 2d8 damage ?
Of course if a deliberately aerodynamic sculpted kite shield existed that could also be a potentially first rate thrown weapon ?