x1 reflects the geography/culture/history of the region constituting central Eurasia, including/especially former Eurasian territory of the Persian Empire, the Eurasian steppes, and regions near the Black and Caspian Seas (such as the modern regions/countries ending in "-stan" (and several others)), in property/aspect x2
This takes into account modern-day developments (unlike, possibly, other names meaning "Persian"). Other potential, somewhat acceptable (although not perfectly so), designations: Central Eurasia, Indo-European region (excluding the western extremity), Turkish-influenced Eurasia, former Timurid lands, eastern Europe with western Asia with the northern Middle East, geographically Caspian-centric Eurasia. Many of these are former USSR territories. These may extend as far westward as nations bordering the Black Sea; they are generally west of China (although weastern and northwestern regions of China may be included) or northern-central India, and possibly extend into the Arabian peninsula. This is a geographical designation for a region and does not pertain to countries (despite the English description or the word itself). The experimental gismu tulnu is used.