I just saw that even Fire Force is available at archive.worldofdragon.org as a cas file, so as far as I know, only tapes that have also audio on them cannot be represented as a cas file, for obvious reasons.
Taking a look at the color computer archive files, the cas files seem to be the same as the Dragon ones. Here you can see a CoCo3 cas file, where the 0x55 bytes are sync or leader bytes, the 0x3C byte is the start of block byte and the 0x00 after that is the byte indicating that the block type is "name". Those are the bytes you see on the screenshot in my previous post.
It would be nice to find a way to automate the test you suggested, but I suspect they'd all work.