I dunno, top 10 might be a bit much.... I can get top 10 even if I auto afk, and I'm a ftp who is stuck on the first group of the sage where all the big ptws are. granted, this might be due to the fact that a lot of ppl gave up sage and just fight once and leave and stuff. But even during the very first Xserver sage, when most people tried, I was, I believe, ranked 4th (it actually got harder to get higher rank because most of the easier targets quit, so I'm basically surrounded by ptw) and then I believe around 5th-7th in the next few (until i started auto afk) As far as i like free stuff, it shouldn't be THAT easy.
I dunno what the average sage size was before Xserver, but I'd guess from personal experience(and the minimal requirement which reduces low * that affect the average) that it's mid 20s to low 30s (there are big ones in S1/S2 to increase it a bit maybe)
Given that, I'd say around 6-8 rewards would be reasonable, as that is how much the participant count scaled. I feel that the same % of population should be getting the reward. Given that some people didn't have sage before, this might actually increase the amount of reward per person over the entire player population.
6 would be ez, 2 of each 1st-3rd price. 7/8 might be a bit more complicated, but a bit extra "3rds" should do just fine.