There are some additional points to consider, one of which is "size" (strength, power, however measured), not the geographical area covered.
EMP is created as one of the effects of a nuclear detonation. The strength of the effect varies with a large number of variables.
Within the area of effect it is known to fry just about everything that relies on a micro chip, and even vacuum tube devices can be affected, it the pulse is close enough and strong enough.
Shielding is protection, BUT, as I understand it (and my understanding might be flawed) if your stuff is shielded against "X", if you are hit with X.1, your stuff is toast.
Home made shielding (assuming it was enough) can only work when what you want protected is inside it.
Unless you know just WHEN an EMP burst is going to arrive, will your vital things even BE in shielded storage??
SO, assume any "modern" electronic anything will be toast. That includes cars with electronic ignitions. Don't assume you can grab a distributor off the (unshielded) shelf, slap in a rig and drive away, either.
And, of course all this assumes you are outside the radius of the physical blast effect AND the radiation.
Don't expect electronic sights to work, if they do, be pleasantly surprised, but don't plan on them working after a high enough EMP pulse.