Hi,
I usually do a culrural region, and then enforce a modifier for sub-groups. Frex Regional Lore (Seshenela), gives you a good area overview, but to know about the Malkioni of that region I would implement a -5% (unles the player was a Malkioni in which case it would be +5%) Modifier, to know about First Age Basmoli of the region a -40%.
Simon