If the only difference is them thin white pads between what you call full contact and knockdown you're already doing knockdown according to IKF and a lot of others rules
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Your issue of taking a lot without giving much back is a sparing issue, not enough of it - I'm guessing you just don't seem to be able to find a gap, the right time the right move? it comes with practice, defending is more natural to most than all out attack, especially if when you have attacked you've caught a few or hit an elbow or similar.
Work on your combo's and try and get them in during you're dojo training sessions - to know if you're ready the answer is as all above have said but also you need to feel 200% ready before hand as on the day 100% of dojo level fighting will be around 50% of what's required to stay on the mat - if that makes sense
