Currently, Rural Polity causes increased food production while reducing consumption for domestic, luxury, and vice goods.
Except the description implies subsistence farming, not the kind of large-scale, highly mechanized farming that would lead to huge surpluses of food. Tartessus has Arid World as one of its market conditions, which is supposed to reduce food production, but it also has Rural Polity, and the tens of thousands of food the market has for sale clearly implies that Rural Polity is completely overrunning Arid World.
Therefore, I propose that Rural Polity, instead of increasing food production, reduces food consumption. This would more accurately reflect a dispersed subsistence farming culture and would hopefully get rid of the OP amounts of food worlds like Tartessus are producing.