A general rule is that any centerpiece should not be blocking the view of the guests so they can still comfortably talk with each other. Centerpieces should also not block the view of the stage or of the guest(s) of honor.
Candle holder centerpieces can be tall or low centerpieces. Generally, low centerpieces should be 12” or lower, and tall centerpieces should be 24” or taller to ensure guests can maintain eye contact while conversing.