I wrote this out to simplify to the rules. I've read and discussed the rules many a time and believe this to be definitive.
How to Use Defensible TerrainEntering and Exiting Terrain can only be done during the move phase and if warranted in the fight phase.
You cannot charge from defensible terrain.
If your formation is larger than the capacity and is normally allowed to enter said feature than treat it as exposed difficult terrain. No defensive bonus.
Entering to Occupy Defensive TerrainTerrain feature must be empty.
One company must be touching the feature.
All companies must be within 6" of the feature.
Once occupied the formation receives a defense bonus and has ended its move.
Exiting a Terrain FeatureIf enemy is within 6" roll for courage. If failed you cannot exit.
One company must be touching the feature.
All companies must be within 6" and be in a legal formation.
Cannot move further but can charge as normal.
For purposes of shooting is considered to have moved at half rate.
Shooting/Spells Cast from and at Defensible TerrainRange is measured from the center of the terrain.
Defenders can trace line of sight from any point on the feature
Defenders use half the capacity and round up the number of companies for direct fire. The rest are considered support.
Defenders are always shot at the front.
Charging Defensible TerrainAll charging companies touching are directly fighting. The rest are considered support.
Fighting Defensive TerrainThe defender always fights from the front.
Defenders use half the capacity and round up the number of companies for direct fighting. The rest are considered support.
The defender can assign those companies to whomever is in contact with the feature.
The attacker receives no extra dice for charging.
If the defender loses the fight and is not steadfast on the panic test then as an addition it exits the terrain as per the rules for 'Exiting a Terrain Feature'. If it cannot legally exit than the formation is destroyed.
The attacker can then immediately occupy the charged feature if empty.
Referencesspiders & terrainWotR: Charging from defensive terrain
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http://drinkingwotr.blogspot.com/ - Links to my CrAzY House Rules, Games and 'poor man's' terrain.