Interestingly, it seems that this "curling" effect is dependent on gravity. I did an experiment where I cooled molten METL down in a gravity-free simulation, and it solidified in the exact shape that it had when it was still liquid. Also, when I repeated it but with a source of newtonian gravity nearby, it did the "curling" effect, except instead of moving upwards, it moved away from the newtonian gravity source.

Use cray to build a wall of shld on top of the metl, melt and cool the metl, use pump to destroy the shld

I got an idea use something that creates negative pressure pulling it down... we need something like anti-thunder from my mod

In addition, it seems that turning off all forms of gravity prevents the METL from cooling the way it does. In a simulation with gravity disabled and no newtonian gravity, molten METL will solidify in the exact form that it had when it was molten.