Actually the diameter of wax that the candle melts is dependent upon the diameter of the wick. Most large candles have too thin a wick and will never burn to their full diameter.

Back in the old days, candles used to be well balanced and you could buy eights, tens or twelves and each would burn properly.

Unfortunately yuppies have entered the candlemaking business and knowing nothing about candlemaking just shove any old wick into any sized candle.