To believe that I needed an example. If the curve starts flat, of course also whales should profit less when upvoting an own article on which nobody else has voted so far.
I was comparing linear to the quadratic curve we had before. I see now that you meant sigmoid. Rewards are calculated by total Rshares contributed. Depending on the exact implementation, a megawhale might just get to the peak all by themselves with a sigmoid curve. Don't underestimate the disparity between whales and minnows - it's enormous. Anyway, it's not possible to talk about details like that without knowing the exact implementation.
I have to say this sigmoid function is 'fascinating' me as it could avoid the disadvantages of the linear and the quadratic curve. Therefore I wanted to attract some attention for this idea and see if some other steemians might be interested, too. :)
Of course the exact implementation is what finally would matter, but before to rack my brain too much, I wanted to plumb if the idea is able to attract some interest.
Anyway: thanks for drawing the attention on diminishing returns again!