I recommend reading the STEEM whitepaper if you really want to go down that rabbit hole.

I'm not really sure what the need to know the details of the reward pool is about.

Let's say your SP investment equates to a glass of water. The reward pool equates the the oceans of the world.

So does it matter to truly understand the reward pool? Perhaps if you were interested in investing $1,000,000 US dollars in SP, then maybe you should fully understand the reward pool. Otherwise, you really should be concerned about keeping up your STEEM friends and your community in good standing. If you are interested in your returns, you should try to vote often and try to maximize your friend's allegiance. Most importantly, provide entertaining and consistent content to gain supporters.

Ultimately, any burning of STEEM, SBD, or any returns to the reward pool has not or will not ever make any impactful difference in the reward pool. imagine adding or subtracting an ant from an ant colony could not possibly make any difference to the overall success or failure of the ant colony.