Politicians and policy experts have paid a lot of attention to those taxpayers who would be exempt from the AMT if the levy is fixed or even temporarily patched. But there is another group that has been largely ignored—those who would still pay the tax but owe far less if the law is patched.

That group would feel relief because a patch would increase the AMT exemption. Ways and Means Committee Chairman Charles Rangel has proposed raising the 2007 AMT exemption from $45,000 to $66,250 for couples and from $33,750 to $44,350 for singles. The Tax Policy Center estimates that those changes would keep 20 million taxpayers off the AMT, leaving about 4 million still paying the extra tax.

Those 20 million folks the patch would fully protect from the AMT would save less than $1,600 apiece, on average, while people still caught by the alternative tax would see their tax bills fall by more than twice that amount, an average of nearly $4,000.

That said, what really matters is the percentage change in after-tax income, and on that count, the two groups would get roughly similar average tax cuts: a 1.5 percent income rise for the "fully-spared" group and 1.3 percent for those still on the AMT. What's more, tax savings would be markedly progressive among households who continue to owe AMT: those with income below $100,000 would see their after-tax income rise more than 4 percent, compared with 3.6 percent for those between $100,000 and $200,000, 2.1 percent for those between $200,000 and $500,000, and less than 0.2 percent for those above that level.

Effects would be much flatter across income groups of taxpayers taken completely off the AMT rolls.  After-tax income would rise between 1.2 percent and 1.7 percent for income categories between $30,000 and $500,000 before again tailing off to less than 0.3 percent for households above that level.