Generally to deflect fast you want to reach the attacker's wrist or ankle in a most possible straight line from where your arms were positioned before you've decided to execute your deflection. If your arms were to the side of your body and the attacker directed a blow or a kick to the center of your body or head you would want to execute an inside defense(inward block or deflection) . This is simply because if you try to do an outside defense, you are wasting time bringing your deflecting arm to the other side of the invisible fence first.
Sometimes in the long range as you lunge to cover the gap you have the time to reposition your arms for a deflection that will occur after you finished the lunge.
However you must tell the students that to be efficient you do not want to take chances and you need to be clear on what is possible and what is not before you get into sparring level.
One of the problems with a technique based martial arts is that when you do not know all the relevant information that is related to one technique or another, you end up applying your technique inappropriately and your system becomes useless for self defense.
Instead your sparring becomes an exciting event where sometimes you are successful and sometimes you are not without ever knowing why. You start to compete against yourself on a daily basis learning to control your constant expected frustration at the most. Is that part of humility?
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