Wow @happyme, thank you very much for your investigations and the great feedback!
You are absolutely right, the slider should automatically jump to the correct position in case of typing in the value manually. That's now on my list for one of the next updates ;)
I will think about your other points over the coming week. Having kind of a threshold for the minimum payout amount could really be a very good solution. It's not so easy to implement, because the beneficiaries can't be changed after creating a post and the account @steemworld.org would need to send the rewards back to the author after payout, but I like the idea.
Sorry to create more work for you, but I suspect you are a bit of a perfectionist so would like to make things as best as possible. Since there are no deadlines to your work, you can prioritize and do only what is most important and leave the rest for later.
I know absolutely nothing about programming, so I have no idea how all that "magic" happens with beneficiaries, but I suspected it would not be easy to wait until pay-out to grab the percentage. It was just an idea and might not be feasible. However, where there is a will, there is a way. It might be more complex, but I suspect you could mine the data of past earnings and create some average. Those who get over a certain average weekly or monthly earning would be affected while the remainder are not. By using past earnings, you also ensure that someone who has JUST broken into the threshold is not immediately penalized. That way if it was a one-time deal where a nice trail passed through, they don't automatically lose some of their earnings. Only when they make consistent good earnings will they need to pay the user fee.