Oops, I seem to have changed the chance of converting grassland jungles to (1 - (1 - featurePercent) ^ 2) some time ago.
featurePercent is 0.30 right now in normal rainfall, so it would be 51% chance of converting.
It's higher chance in Wet maps, so the map isn't entirely flooded with 3 tiles.
Whether FeatureGenerator should also follow rainfall is your decision. Not every map has rainfall option, and rainfall might not affect terrain/feature generation in every map.
featurePercent is 0.30 right now in normal rainfall, so it would be 51% chance of converting.
It's higher chance in Wet maps, so the map isn't entirely flooded with 3 tiles.
Whether FeatureGenerator should also follow rainfall is your decision. Not every map has rainfall option, and rainfall might not affect terrain/feature generation in every map.