The whole point of this event is that they know exactly how the number work while the majority of players dont (and afraid of it) so they create this event as encouragement.
Refinement is not that hard, especially when the chance stop deteriorating from 51% onward. I made 1 +20 with 8 pot left on first day (went 22 and got 2 fail) and my friend made +25 with 1 pot left yesterday. I couldnt get it over 10 now but overall now i know my chance of hitting 10+ is pretty high.
In fact, after getting my first clover to 20, i gathered the courage and went 11 on my Viena Mace (not as lucky as the clover but enough)
When thing come down to chance, there gonna be bad day and good day, you just have to live with it.