There's your problem. If food is one of your major expenditures then the FT will hit you harder than a household with no kids - especially in a Sate that does not now sales tax unprepared food. Even if you account for the prebate. A mother of 4 teenage boys will never buy into the FT since she does not want a adjusted gap increase in her food costs. There is no way the purchasing power will stay the same. Virtually everyone is different.
It took years for Wal-Mart to break into the food industry. Why? Because of the way food is distributed. They have taken lower margins on food than a traditional GS and some suppliers have stopped doing business with them. Their ability to buy meat has been hurt because of their practices - for example.
The mother of 4 will get a prebate to compensate for the tax on poverty level expenditures. Those who consume a large percentage of their income will pay a larger percentage of the tax. Those who save and invest, will not.