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From AGEWiki

An Area defined in Units and Models to regulate 'away from home' behavior of Units and Models

Exported parameters are Effective for game engines dated June 7, 2012 or later:

The test on HomeArea is always done at the element ( = model) level. It concerns discipline, cohesion and move speed for a non leader, and abilities, ratings for a leader.

A model will be at home if the area he is in is the one specified in HomeArea, in Models DB or in Units DB. If one is correct, then the Element/Model is at home.

A model is considered 'Outside Home', if he has a home and is not at home. This means that if you specify nothing (no HomeArea in models.xls and no HomeArea in units.xls), then he is never at home, but never outside home either!

If outside home, the 6 variables starting with 'area' applies, as penalties. If at home, the last variable, cohLocalAreaBonus applies.

In additions, Militia and Irregulars are considered 'outside home', if they are out of their area of recruitment (value Area, at the units level), but generally this is equals to HomeArea...

HOME AREA PENALTY/BONUS 
// see HomeArea at the model level
areaOutsideHomeAbi   = -1 // -1 level to abies (can render them inactive)
areaOutsideHomeStr   = -2 // Strategic
areaOutsideHomeOff   = -2 // Offensive
areaOutsideHomeDef   = -1 // Defensive
areaOutsideHomeTQ    = -3 // TQ (and 5 time that to max cohesion)
areaOutsideHomeMR    = 66 // Move Ratio Coeff (x0.66)
cohLocalAreaBonus    = 10 // bonus to max cohesion if at home

Note:

These parameters are the default penalties for older game versions using the HomeArea
parameter in Models, and/or any AreaBound abilities in Models

Note 2:

It is strongly recommended that HomeArea be defined only in Units or Models, not both.