The affix ṅīp is not used to denote the feminine after a bahuvrīhi samāsa ending in an,
This refers to those Bahuvrihi compounds in which the penultimate is not elided. Of the Bahuvrihi compounds which lose their penultimate letter, it is optional to employ this affix or not; as it will be taught in (IV. I. 28). Thus सुपर्वन् 'possessed of beautiful joints' is both masculine and feminine. As सुपर्वा, सुपर्वाणौ, सुपर्वाणः; so also सुशर्मा, सुशर्माणौ and सुशर्माणः ॥ In these cases the penultimate अ of वन् or मन् is not elided. See 6.4.137.
Why do we say \after Bahuvrihi compounds\ ? Because after any other compouds, this rule will not apply. As अतिराजन् is an Avyayibhava compound, its feminine will be अतिराजी ॥,