I think people missed a joke here. I mean, seriously, EY is not so stupid as to think that it is 4 bits literally. And if it is 4 symbols, and symbols are arbitrary size, then it's not 'plus a constant', it's multiply by a log2(nsymbols in alphabet) plus a constant (suppose I make Turing machine with 8-symbol tape, then on this machine I can compress arbitrary long programs of other machine into third length plus a constant).

No, really. It can be 4 literal bits and a sufficiently arbitrary constant. It's still a joke and I rather liked it myself.