Have you thought about advertising through Patreon? Basically, people "subscribe" to your books, by pledging a certain amount per book. When you come out with the material, the money is automatically drafted from their accounts.
It would help give you a steadier promised income, and Amazon wouldn't be taking a cut out of your loyal customer base (not sure what Patreon's cut is). And, if they feel like giving you more for your great content, they can choose however much they wish.
Anywho, here's a youtube animator that is promised $3,500 per video through the site:
https://patreon.zendesk.com/hc/en-us/articles/204606125-How-do-you-calculate-fees-
5% seems way cheaper than Amazon.
A lot of folks do the Patreon to help pay their way with video releases. Sailing folks. Never heard of a book angle but it makes sense.
