I use 4630 and rub into slightly sunken tops only with larger diameter containers. While it's supposed to be a single pour wax, it does shrink a little. Why yours are behaving as they are I can't explain. I heat to 185, add cold FO, heat to 180, stir, and pour at 175 into cold containers. The containers are nestled on a cork mat and left to cool. I am not a believer in curing but do wait a week to test burn. Not all FOs will work in all waxes. To test if it is the wax or your system, make some melts and test those. If you get good HT, then your system is not optimized and, most likely, you need to find a different wick. I find that a weaker burn works better than a more vigorous one.