Iran is also considerably more mountainous than Iraq, if one looks at a topo map of Iraq and examines all the generally 'flat, somewhere generally near the Euph

Iran is also considerably more mountainous than Iraq, if one looks at a topo map of Iraq and examines all the generally 'flat, somewhere generally near the Euphrates' area vs a population density map in people per square km. Yeah there's more complicated terrain in the northern part of the country, but nowhere on the size/scale of what exists in Iran.