What is the test for obtaining an award of attorney's fees from the Government?

In order to recover an award of attorney's fees from the Government, a tax litigant must qualify as a "prevailing party" under section 7430(c)(4)(A). "First, the litigant must 'establis[h] that the position of the United States ... was not substantially justified.' Second, the taxpayer must also 'substantially prevail[ ]' with respect to either 'the amount in controversy' or 'the most significant issue or set of issues presented.' 7430(c)(4)(A)(ii)." Heasley v. Commissioner, 967 F.2d 116, 120 (5th Cir.1992) (emphasis in original).