Normally I give mine several burns before determining a wick size. I have a few FO/wick combinations that I don't get a good burn on until about half way down the jar. The heat buildup in the jar seems to help melt the wax faster. So a wick that may not have looked good at first, sometimes will catch up, halfway through the jar. The only times I switched wicks was if I was way off base on the one I chose. If that happened, I would melt the candle back down, dump the wax back into the pot, wipe the jar and rewick it, repour the wax and let it set back up and retest. I tried just yanking the wick once, but could not get the new ones to stand upright long enough for a good burn. There are lots of ways to test, you have to do what works best for you, what you think is going to give you the best results.