This might be a dumb question, but is there supposed to be a pice of wood on top of aqueon stands? I have a 90 gallon and stand, and it seems to just sit on the top edge of the stand rather than inside this 4 inch lip. It looks as though it's meant to sit that way, but it stills looks a bit unstable compared to stands with covered tops. Before I fill it I want to make sure it's supposed to be that way. Any thought on this would be great.