Terrain (Total) indicates that a model receives +1" when in any type of terrain, but is that only when it's unusual terrain? I saw someone on this forum suggest that you simply get +1" movement because it applies to all terrain. For example, a Ninja would get MOV 5-4. I'm not sure that's how it works - do you only get the bonus when you are in unusual (desert, Zero-G, Mountain, etc) terrain or all the time?
you only apply it to the actual special terrain locations. see the last bullet point in terrain. all special terrain areas must be marked. and the characteristics must be agreed on by all players. the only way they would always stay 5-4 is if the entire table was a special zone.