The Lunar Heartlands are about 10 times the area of Sartar, with 25 times as many people. To the south of the Lunar Heartlands are the Lunar Provinces, a series of client kingdoms (most originally Orlanthi) centered on Mirin’s Cross. War is common in the south and many Heartlanders just consider the south to be the Land of War. Warlike and adventurous people are sent there to make a name and reputation for themselves – and also to keep them from being trouble-makers in the Heartlands. It is a dumping ground for misfits, malcontents, and others, where they can serve the imperial interest rather than cause problems.
To the west are the West Reaches, the rump of what used to be Carmania. They have long been extremely peaceful, protected by the Syndics Ban. However, Lunar priests and magicians warn that the Ban is lifting and none know what will be revealed.
To the north are Lunar allies – Thrice Blessed (aka Eol), the Char’un Pure Horse People tribe, and the Blue Moon trolls. They are also peaceable. The real concern is the east – Redlands and Pent. This nomads of Pent have recovered from the Nights of Horror and now raid the eastern satrapies. They reject the Lunar Way, and now many embrace Orlanth and Storm Bull to fight against the Lunar Empire. Many tribes are unified together in a big confederacy called the Voor-ash.
So whenever you think about Lunar activity in Sartar, keep in mind that it usually just part of the Land of War – the southern reaches.
The Heartlands are the Land of Lunar Light. It is where the Red Goddess is manifest directly above, where the Red Emperor resides, and the deeds of the Red Goddess took place. From the earliest sources it is the Heartland Sultanates.
Although the Seven Mothers is a missionary and proselytising cult, Sartar, Prax, and the Holy Country are a long way away from the main cult centers. And the Lunar Heartlands and other major centers of Lunar civilization still have a lot of work to do to get them to all embrace the teachings of the Red Goddess. It is much easier to be a Seven Mothers missionary in Doblian or Sylila than in Tarsh, and far easier to be a missionary in Tarsh than in Sartar or Prax!