I always heard that a 20t granny would not fit on a 4 arm 64mm crank. There in a review for a 20t Boone titanium ring and here is a link to order.
I'm considering getting one for the Deus crank I just ordered.
Mtbr's 2016 Winter Biking GearReviews and Roundups
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Thread: 64mm 4 arm 20t