All missile bodies except ramjets are pretty much all exact matches of each other. This new missile looks to be wider and longer than the PL12.
If it keeps the same (or a near identical) body/width ratio then that would explain how PL-12 superimposes over it so perfectly, but we have no way of reliably telling if it is that much longer and wider. I could only be by a measure of a few centimetres and that would make all the difference but at this distance without a fixed variable like J-20s length or dimensions of the weapons bay, I feel a bit stuck