High attacks can be block standing or ducked by crouching. High attacks tend to be horizontal attacks and are usually great for hitting opponents using lateral movements. High attacks can be blocked standing or ducked. This means the attack hits in a mid range region. Mid attacks must be blocked standing and can not be avoided by crouching.
Most mid attacks are vertical attacks and thus easy to evade with lateral movements.
All mid attacks must be blocked standing. Like high attacks, low attacks tend to be horizontal attacks and the best means to evade a low attack is to jump over it. Low attacks must be blocked crouching. Special M attacks are usually very fast or highly effective thus the reason for the simple guard. Special M attacks can be blocked standing or crouching.