Reading the exact same doccumentation pointed out in the reference, I deduced that the result should be 'x' for the single char column, and 'xxxx' for the longer column, but that was deemed incorrect.
Naturally, I had to actually test this in reality, and Lo and behold! My interpretation of the documentation seems to be the correct. The number of X-s track the length of the column up to a maximum of 4 characters, after which it stops increasing.
Just because you're right doesn't mean everybody else is wrong.