I have a real pet peeve about centerpieces not blocking the guest view. The flowers should allow the guest to make eye contact across the table. There are exceptions to this. A 72 inch round table is too big for people to talk across. People may not be able to talk, but hopefully they can see each other. There is a test to see if an arrangement is going to block the view. You put your elbow on the table the arrangement is on. Extend your arm up next to the arrangement. If the flowers go above your middle extended finger (no not that!), they are too tall! Now you know a trick of the trade!