Centrepieces on top table?

In my wedding addled mind i was just going through what we have and havnt got sorted and the centrepieces came up. We have several vases and bits to fill them and feathers and so forth and have made a mock up for a "normal" table centrepiece and they are relatively tall, but not as to impose on people's view, however when thinking about the top table where would you place these? We have 6 on our top table and was thinking of putting one either end of the table but wouldnt the middle look bare? Advice lovely ladies ??