One thing to consider that doesn't seem to be covered is that nuclear war planning is focused on a diplomatic outcome, not genocide. The fastest way to a diplomatic resolution is through economic means. As a result, it seems reasonable to conclude any nuclear attack will target the productive cities and regions of the target country necessary to cripple their economic system. The US Homeland Security agency has a map of these locations produced some 30 years ago by the military that is still largely valid. The locations most likely targeted coincide with but do not exactly correspond to population centers. In the US, they include Atlanta(trade and shipping) Kansas City(production). Cities that produce more customers and consumers than producers are of more value alive, as their now unmet needs will pressure favorable decisions. Targeting of military facilities will also be limited to focusing as much allocatable firepower on suppressing the retaliatory strike potential of the enemy. At the final negotiating table, ones position is as much dictated by ones own productive assets as they are by the opponents losses. A nation whose productive capacity remains intact is in a favorable position militarily as they can afford to subsidize and fabricate more resources for any extended war.So, given that any weapons used will be likely divided between destroying production and protecting production, the vast majority of people, especially those in rural environments and smaller cities, will likely not be at direct risk. And since the vast majority of the industrial regions are made of concrete and steel and other non-flammable materials, it also seems less likely there would be any substantial firestorms.
When modeling the total destructive potential of any arsenal, i also would presume that any combatant is likely to minimize their usage of warheads so that only a safe level of redudancy is employed, and a large stockpile remains on hand as a strategic deterrant to third parties not part of the initial exchange. If america, say, were to be in a war with either russia or china, they would likely retain enough warheads for a MAD scenario involving the other nation, and russia would retain warheads for europe, and china for india.The same may not be true of "salt the earth" type genocidal wars as are possible in nuclear exchanges among the smaller countries where hostility is more about fundemental differences in ideology and race..