I get 3 food in irrigated tiles when the rules should be:
Each worked tile that gives more than 2 food,shiled trade will suffer a -1 penalty, unless the city working it is celebrating.
The reason why this one is tricky in the test games is that some players have started at an earlier turn and have already researched techs. Once any player invents the rails that invention will cancel the penalty for every nation. Usually everyone has already switched to some other form of government or built the pyramids but in test games this is usually not the case.
About the map. We will make some more map test prior starting the game so we may or may not use the current type of map for LT37.