[Facts] Re: Pronunciation of -iva (derived from Old English gifu) names
The emphasis is on the "EE". the first syllable is short and less emphasised, resulting in the reduction of the original disyllabic sunna- to sunn-.
The second element gif- (the ending originally varied by declension) loses the /g/ as this was palatalized to /j/ and merged with the following /i/ (and further contributing to the loss of the /a/ of Sunna-). The modern hard /g/ in give and gift were reintroduced from the continent in Middle English.