I've never heard Micaiah pronounced "mie-KAY-ə". I know a family with a son named Micaiah, and his name is pronounced "mih-KYE-ə" ("mi-KIE-ə", using this site's pronunciation guide). I also know of a girl Micaiah (friend of a friend). I'm pretty sure she pronounces her name "mi-KAY-ə" (like Michaela without the L). "mie-KAY-ə" sounds really awkward.