What distinguishes the final nūn of تَفْعَلِينَ and تَفْعَلْنَ?

Complete Imperfect Paradigm: Active, Passive, Affirmative and Negative

• Both are nūn al-niswah
• First is inflectional nūn, second is nūn al-niswah
• First is nūn al-niswah, second inflectional nūn
• Both replace tanwīn