The E1 pulse from the EMP weapon (the pulse that damages integrated circuits) is generated by Compton effect electrons in a layer of the atmosphere at a range of between 20 and 40 km in altitude. The burst point needs to be well above this range in order for the gamma rays from the fission to all enter this layer at roughly the same instant.
A burst at an altitude of 60km (about 38 miles or 200,000 ft) gives the E1 pulse a footprint with a radius of about 630 miles.
The problem is not affects on Israel (900 air miles from Tehran) but rather on Bagdad (400 miles) and US forces in the Persian Gulf (400 to 600 miles).
One wonders if it can be "directed" in some way. If bomb-pumped x-ray lasers are possible, perhaps such focussing could be done in the first microseconds of explostion, before the focussing structure is mechanically destroyed.