I know, it's an oversimplification. Timing is involved and it's a curve, not linear. But SteemAX is automated so it attempts to upvote as close to the 15 minute mark (15 not 30 as of HF20) as possible, something a human cannot always do. And regardless of whether it's a curve or linear, the concept remains the same: those who upvote biggest and closest to 15 minutes will receive the largest share of the curation reward. ;)

Rewards increase with the square root of the growth scale of the post.

Rewards increase linearly with the worth of the vote. The more steem power you have the more profits you will have.

If you vote late a trending post the reward is v/8 no matter the value of the post.
If you vote after 30 min, and you are the first voter you will receive a minimum of v/4, no matter if the post is popular or not.

At 30 minutes you get all the reward, but if you vote before the gains decrease with respect to time. The rule to upvote before 30 minutes is: If you believe that the post will grow greater than 900/Dt² times (where Dt is the time in minutes) then it is better upvote.

And so essentially we agree, the bigger the upvote at the 15 (not 30) minute mark on a quality post will earn the highest curation reward. This is the only concept needed. ;)