The word īṣat 'a little' is compounded with a case-inflected word which does not end with a kṛt affix and the compound is tat-puruṣa,
It should be stated that the word ईषत् is only compounded with words expressing qualities (adjectives), as ईषत्कडारः 'a somewhat proud.' ईषत्पिङ्गलः 'a little brownish.' ईषत्विकटः 'a little hideous.' ईषदुन्नतः 'a little raised.' ईषत् पीतम् 'a little yellow.' ईषद्रक्तम् 'a little red.'
Why do we say 'with words expressing qualities'? Observe ईषद्गार्ग्यः ; there is no compounding here.,