One simple tip that might help you be more calm on defense is to just always block low by default. You can see most hops and overheads coming and block them on reaction.
Also, try to be more active with your movement. This isn't a game where you try to maintain a specific spacing for a long time, KOF13 is a game of high mobility and situations that last an instant and then the players are elsewhere already. You should also try to maintain control of your own airspace more with short hops, so people can't just hop in on your face when you do the opening trigger 100% of the time (which you shouldn't)