Hm, the case with only one winner is, that people who think that they'll have a less-than-perfect chance of winning the reward, might choose to chime out, instead of in.

A 2nd and 3rd place + reward might have a positive effect in regards to participation, as people might take a chance and enter in the pursuit for the 2nd- or 3rd place + reward.

On the other hand: one big, fat 🏆 can be enticing in- and of itself... 🌝

I'll gladly accept your offer on chiming-in on the (fixed) amount, we're off for a solid start in that regard!