Generally, unless your target is underground (e.g. a bunker or a heavily fortified emplacement) the goal is to detonate a nuke at an elevation that maximizes the blast. Higher yields would mean a higher elevation required for maximum effect. I haven't been in the know for many years about the construction of ICBM's (I was on the USS Georgia in 98) but those were very high yield Tridents. The amount of fissile material they contained (that would cause the irradiation or "nuclear winter" people refer to) was generally thought to be low enough that the vast majority of it would be consumed in the blast after detonation when exploded at the altitude they would provide maximum effect at. Thankfully, our theories about habitability following detonation remain only theories as this unspeakably horrendous event never actually occurred.
"The assumption that animals are without rights, and the illusion that our treatment of them has no moral significance, is a positively outrageous example of Western crudity and barbarity. Universal compassion is the only guarantee of morality."