With only 30 skill points separating top 10% and top 11%-30% otherwise identical event rewards, I hope completing the 12M milestone diamond track is enough to land in either range.
RNG secret tip: save your deployment character relics until you have at least 4. Last two times I did this I got a Diamond Beowulf and a Gold Filia. I may be delusional, but it looks like a multi-open bumps the luck up.