There is some confusion, I think, due to a similar word: shinza 神座. The confusion arises because the kanji 神 is also read "kami". If you don't know that the correct reading for 神座 is "shinza", and you've heard the word "kamiza", it can be easy to assume that "kamiza" is written 神座 and/or that "kamiza" has something to do with 神. But while the two "kami" are etymologically related (along with 守 meaning "lord, guardian", and 髪 meaning "crown, hair"), in modern Japanese the meaning and usage is quite distinct. "Kamiza" is not even listed as an alternative reading of 神座, and 神座 itself refers to the resting place of the kami in a Shinto shrine
As soon as I read your explanation, I felt my Japanese teacher reach across the years, slap me across the back of the head, and scold me for mixing kun-yomi and on-yomi in reading a single word.
Very helpful explanation.