The value shown is the value of the 50/50 split of sbd to steempower. The sbd is determined by the value of steem so for instance if steem is worth 2 dollars and the payout shows $10 you’ll get half of that as steempower 2.5 and the other half as sbd where you get 2x sbd per steem due to the current value of steem so you get 5 sbd. However this is before the 25 percent curation and if in dtube 25 percent dtube gets. So you’d get only about 2.5 sbd and 1.25 steempower for a $10 dtube post. And then of course as you said if there are more votes during a reward block the amount of rewards goes down.