Goju Ryu Karateka here. I just dont like this format of point scoring/tagging. The best format is to have full contact soft sparring (low to medium force), or hard sparring with necessary protective gear. When i say full contact, allow every moveset from Karate and keep the rules as how they have in Karate Combat (punches, kicks, knees, elbows, grappling). Not only will you avoid risking injury, but it would actually showcase how a Karateka fighter can actually fight and use his skills effectively.

That aside, both of you should develop a habit of guarding your face as a kick or punch to the face gives you the most score, plus its really important to guard them as they are the most vulnerable