If a player decides to leak information which may reveal their alts, I won’t stop them 
But I try to be careful to ensure the game doesn’t leak anything such info.
A typical example is the handling of a lost connection when having multiple alts awake; they will not be put to sleep at the same time (which would be quite revealing), but will individually timeout sometime within a 5 min period.
So, I agree. Block would need to be Character -> Character, while mute can be Player -> Character.