So even if it were productive to calculate intensity based off of 1RM (which it is decidedly not) 64% is way too low. 64% of a 1rm is something that you could in theory do for close to 12 or 15 reps or maybe more because the further you get away from a true 1RM (which again we have no idea what this number actually is because we are working with a novice) the less accurate these formulas become.
A 5RM is supposed to be around 85% of your 1RM. Granted the novice is doing it for sets across so it's not a true RM as you indicated but it aint that far off either!
Ultimately you should let your recovery and tolerance dictate the amount of load used during recovery from an injury not an arbitrary %.
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