The affix tva comes in the sense of of 'nature or action thereof' after the word brahmaṇa denoting a kind of hotrā priest.,
This debar छ. Thus ब्रह्मणो भावः कर्म वा = ब्रह्मत्वम् ॥ This debars तत् ॥ When ब्रह्मण् means a Brahman, by caste, we have ब्रह्मत्वम् or ब्रह्मता ॥
So much for the province of the affixes मञ् and स्नञ् 4.1.87.,