This is just the same behavior as on any other Linux/Unix box with OpenSSH, as long as we are not talking about SMB appliances.
ssh_config is for the SSH client.
sshd_config is for the SSH server.
If you you not specify any ciphers in that file(s), the defaults apply.
See defaults/supported ciphers here:
When changing these on versions prior to R81.10, please take care of:
When running at least R80.40, a quite good hardening suggestion would be for example:
Just before hitting the "reply" button, I saw you are on R80.30. Thats sad, because that means you are limited to the possibilities of the very old OpenSSH version CheckPoint uses before R80.40, as PhoneBoy said already. Please see sk165685 for supported ciphers. The list is very short, but you can use ctr and get rid of cbc by specifiying only the ctr ciphers in your Ciphers string:
Not sure about Kex, MAC and HostKeyAlgorithms support in R80.30. Its not documented on sk165685 and I do not have access to anything older that R80.40 at the moment to look up myself.