Smaller yield warheads maybe. The relative effective size of the warhead compartment will not be ten times larger than something like a DF-31. 30 warheads will be 30 smaller warheads. Unless Russia has minitiarised nukes better than both China and the US, I'm not going to believe their ICBMs and warheads are truly just that much ahead of everyone else. Everyone spends roughly the same amount on military each year (as in not like NK who spends around 20% of GDP).RS-28 is a liquid-fueled missile what has size of an space rocket, so of course it can carry huge payload, remember that original R-36 Satan (RS-28 is supposed based on it) could carry over 30 warheads if needed.