If a candelabra will be used at a dinner table, the candle should be much higher or lower than your guests' line of vision. If the candle is eye-level, the flicker of fire will be distracting and irritating during the meal. A taller candle will allow a longer burning time, while a shorter candle ensures that it will never melt to the point of becoming an irritating height.
If the candelabra is going to be used for decorative purposes, the candle height is not as important. Choose a height that is aesthetically pleasing and will not drip excess wax onto your table.
The clear rules of etiquette for candle length apply only when the candelabra will be used at the dinner table. If your guests won't be disturbed by unwanted light in their eyes, the length of your tapers is a matter of choice.