Hi there, I also train kapap and as the other guys, I agree, any grapling system is a good compliment since there aren't too many ground techniques in kapap. Even when is better to stay away from the ground, sometimes you'll find yourself in that position and won't hurt you to know what to do, even if it's only to get back on your feet. What I do is a little BJJ, but any system with ground techniques will work.
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"I don't need to fight to prove I'm right"