If you don't mind a marbled texture and you have a "6 pack mold" spray the inside of the mold with Pam or a generic and put them in a pan of ice water
as you fill them, you'll get a hump instead of a divot.
Now if you're using them for light and or heat, get some 1/4" cotton rope and soak it in a pint of water with 5 tablespoons of borax dissolved in it, let it dry a while and put a washer on the candle end and use a tuna or roast beef can as a mold. it makes the equivilant of an all night storm candle and the tins themselves can be painted with elemental or festive colors like day glow orange so you can find them, then after they cool, stretch saran wrap over the top and tape it in place or use a rubber band to keep out wax weevils and to keep the wick clean.