The received logout message is compressed, so this number is the multiplier of the original size of the logout message to compute the size of the buffer where the logout message will be decompressed.
It's somehow the decompression factor.

For the buffer, we could also have a fixed size for the buffer (like 10k), but I thought that ten times would be a sufficient mutiplier...

Let's make a real test:
```                String sessionIndex = "ST-45-fs45646r84ffs1d31f554f5d4f64fg6r8eq5s4d6f4fddsf46-cas";
        String bm = LogoutMessageGenerator.generateBackChannelLogoutMessage(sessionIndex);
        System.out.println("bm.size = " + bm.length());
        String fm = new String(Base64.decodeBase64(LogoutMessageGenerator.
                                            generateFrontChannelLogoutMessage(sessionIndex)));
        System.out.println("fm.size = " + fm.length());```

And the result:
```bm.size = 354
fm.size = 224```

So ten times is enough, it's even too much...