The monthly pool of money allocated retroactively to self-published authors whose work is offered through Amazon’s Kindle Unlimited subscription plan rose again for December — both in the closely-watched per book payout, which was $1.43 per borrow/read, and in overall dollars, with Amazon allocating a $4.25 million “bonus,” making the total pool for the month $7.25 million. Per book payments hit a low for the year of $1.33 in October, then rose to $1.39 in November. The December unit fee is still lower than the August and September payouts. The December pool accounts for roughly 5.07 million borrows in all. […]