On warhead miniaturization, I think I have found some indirect evidence pointing towards China's progress since 1996.
The DF-5C test in 2017 was, according to the Americans at least, a test involving 10 MIRVs.
The throw weight of a DF-5 is 3000-4000 kg, including non-warhead coponents like the electronics or decoys.
Thus, each 535 warhead should weight no more than 400 kg. More likely somewhere around 360-380 kg.
DF-5C supposedly is armed with improved DF-31 warhead. Original had weight of 470kg and yield is said to be around 500kt not 1MT as ofthen claimed by many publications what get their info from old 1992 New York times article.
Seems to me that China has at least two warheads in service. Improved DF-31 warhead and then something smaller with 90-100kt yield.