There are no options to select for optimal EMP altitude so maybe that would be higher but can you really imagine an enemy launching a nuke at us and be focused solely with EMP effects?
The "high altitude" EMP detonation ShootistPRS is talking about is in orbital space, at the edge of, or even outside the atmosphere. This is an ENTIRELY different thing than an airburst at 2 miles up, which is INTENDED to cause destruction on the ground. The edge of space detonation is 10-12 miles higher up, and this distance makes a huge difference.
Yes, I CAN imagine an enemy launching an EMP strike, in fact I can see them doing it, IN PREFERENCE over a conventional airburst or ground burst.
In fact, its almost the perfect strike against a modern enemy. Clean (no fallout), doesn't destroy cities, buildings, or leave large burned, areas. Direct loss of life is virtually zero. (as mentioned, those who need electricity to survive because of a medical condition will die when the power goes away, but the rest of the population will not be physically harmed by the EMP)
It's rather elegant in its own way. With one good "zap" you send your enemy back to 1800s technology, and you do it without destroying cities, or killing people in job lots. NO Hiroshima type effect, or death toll.
IN fact, its quite likely that whomever the target is, the people will be "in the dark" not just because the lights go out, but also about who attacked, where, and why. The WHEN will be obvious, but nothing else, and there will be NO modern communications net to distribute information. What ever we wind up with as a functional government after the ZAP won't even be able to know the will of the people any more rapidly than the pony express can deliver the mail.
Another effect of the ZAP, is that our economy WILL collapse. On the plus side, you won't have to worry about paying your credit card bills for a while, but the down side is any "money" that isn't a physical thing is simply gone.
Billions and billions of dollars will simply cease to exist. Everything in electronic transfer at the time of the ZAP, gone without a trace. Money in banks won't be useful for a while, either, because anything not written on paper will be gone, and without records of who owns what, they can't give out anything to anyone. So forget about taking your money out of the bank, as well, and that's assuming the banks are even open.
So, while a ZAP attack would be a very, very bad thing, it wouldn't leave smoking craters where cities once stood, nor hundreds of thousands of dead and dying as constant reminders. That might be enough to convince some unbalanced fanatic that it would be worth the risk.
Personally, I think anyone who did take the risk would learn what the Japanese learned after Pearl Harbor. That in the end, we don't quit. There would be no negotiated peace, until AFTER the aggressor nation was wrecked, up to and including nuclear fire as a "persuader".
and, then, there is the rest of the world. An EMP strike is still a nuclear attack. Weapon of Mass Destruction. We have treaties, and beyond those we have "gentleman's agreements", and beyond those there is simple self interest, so I doubt the rest of the world would simply sit back and watch. Many would, but some will recognize the necessity of "shooting the mad dog" to preserve themselves.
Again, not something I am personally going to worry about, but something prepper types (who used to be called survivalists) might want to consider.
And paper money won't be worth much, if anything, either.