The horde-ing mechanics are mostly determined in the descr_sm_factions:
Code:
faction f_parthia ;;; Faction number 11
culture cul_4
religion rel_b
symbol models_strat/symbol_f_parthia.CAS
rebel_symbol models_strat/symbol_f_parthia_rebel.CAS
primary_colour red 115, green 77, blue 124
secondary_colour red 115, green 77, blue 124
loading_logo loading_screen/symbols/symbol128_f_parthia.tga
standard_index 8
logo_index FACTION_LOGO_F_PARTHIA
small_logo_index SMALL_FACTION_LOGO_F_PARTHIA
triumph_value 5
custom_battle_availability yes
horde_min_units 20
horde_max_units 60
horde_max_units_reduction_every_horde 15
horde_unit_per_settlement_population 250
horde_min_named_characters 1
horde_max_percent_army_stack 80
horde_disband_percent_on_settlement_capture 30
horde_unit steppe cavalry parthian early general
horde_unit steppe cavalry parthian early general
horde_unit steppe cavalry parthian cataphracts
horde_unit steppe cavalry dahae horse archers
horde_unit steppe cavalry dahae horse archers
horde_unit steppe cavalry dahae horse archers
horde_unit steppe cavalry dahae horse archers
horde_unit steppe cavalry parthian horse archers
horde_unit steppe cavalry parthian horse archers
horde_unit steppe cavalry parthian horse archers
horde_unit steppe cavalry dahae skirmishers
horde_unit steppe cavalry dahae skirmishers
horde_unit steppe cavalry dahae skirmishers
horde_unit steppe infantry gundi nizagan
horde_unit steppe infantry gundi nizagan
horde_unit steppe infantry gundi nizagan
horde_unit steppe infantry gundi nizagan
horde_unit eastern infantry kavakaza kofyaren
horde_unit eastern infantry kavakaza kofyaren
horde_unit steppe infantry parthian archers
horde_unit steppe infantry parthian archers
horde_unit steppe infantry parthian archers
horde_unit steppe infantry parthian archers
can_sap yes
prefers_naval_invasions yes
can_have_princess no
has_family_tree yes
We tinkered with the red lines to reduce the reported "horde-spam" with earlier versions of the mod.