I found 100% Soy pillar candles can't take the heat and just end up collapsing half way down into a mess I have brought some off another candlemaker and they did collapse and make a mess For this reason I am not even going to attempt a 100% soy pillar
I have used the molds with the rubber bands and they are fine, the wax doesnt spill or anything Some of the molds that don't have bands are so thin and rip
How about double wicking it? I have never found a wick that burns good in a heart candle They either burn and leave 1/2" gap as your pic, or drip over and make a mess