Ok here is my preliminary assessment of the weather/terrain modifiers.
There is no such thing as fort_defense, river_defense or shore_defense (or paratroop_defense), so these will have to remain as penalties to the attacker.
-40-50% seems reasonable for river and shore attack, with say 25-30% bonuses eventually applicable from tech.
-50% should be as low as it goes (except for night)... the only other penalty that will be applied is the leader penalty, which is out of our hands.
Fort attack I am a little unsure of... is it a hard-coded penalty based on the level of the fort? Anybody know? Does it need to be lessened?
Alright next all terrain and weather ATTACK penalties need to be eliminated, or greatly minimized. For example, I would retain small attack penalties (-10%) for winter (snow, blizzard, frozen) and for jungle and desert, which can be mitigated by acheiving the appropriate techs.
Once that is done, positive modifiers for the defender need to be applied. In this case we should avoid going over +200% combined modifiers (for example, you might get +80% for mountain and +80% for blizzard, for a total of +160%, and with level 6 leader that'd take you to +190%, or 290% defence efficiency, while the attacker attacker labours at 120%.)
Now I don't really LIKE giving a positive modifier to the defender for weather (since combat intensifies instead of dropping off), however hopefully it will encourage the attacker to cancel or break off attacks, and thus result in less overall combat that way. The higher losses in actual combat can be explained by weather-related attrition.
Some testing needs to be done to determine what the base modifiers are. I might have time to do some of that tonight. The weather modifiers are going to be a hell of a job... I'm kinda hoping the spreadsheet snippet I displayed in anothe thread is accurate
