If 'Seanio' is a proper noun, it's pronounced the way the person pronounces it (if it's a person's name), or the way the locals pronounce it (if it's a village, etc.)
I don't, perhaps because I lived for a long time in Ireland and I study the Irish language, I pronounce "Seán" shorter. Unfortunately I don't do phonetics but I would say it's closer to "shone" (past tense of shine) but "drawled".