Yeah, once you skip a day it's hard to get back.
I'd advise it to be highest yield ,and not ROI.
No need to set minimum odds or minimum amount of picks.
Only prematch picks count.
If it's a specific sportsbook it's hard because some users are limited at some bookies, not all bookies have the same offer, and so on.
Minimum amount of picks is not very important but it is put in just as a fail safe so that a contestant's skill is averaged out to an extant over a course of time. Also, to keep the spirit of the tournament going. I'll give you an example. Lets say a player bets 20x as their first bet and wins. He might just stop betting altogether after that and react based on the competitors. The other way works as well, if you lose 1 bet, the min limit give you hope to carry on betting as there are 19 more bets to go and you'll surely win a fair few from them.
Also, can you explain what do you mean by yield? I had chosen ROI instead of +profits because from my testing, every other potential gauge can be exploitable. Lets say, we just calculate the difference of the stack from start to end. A person with 1 BTC will have a major advantage over a person with 0.001 BTC with respect to how much profit they've made. Please let me know. Once I'm done with the first installment. I am very much looking forward to host another contest which would me bigger and better. Could surely help the cause if you have any feedbacks on how to improve the current format.
Yield:
(aw - ab) / ab x 100%
where:
aw - Amount of winnings (how much money a player won)
ab - Amount of bets (how much money a player invested)
When you calculate ROI, the player that had a lot of bets on smaller odds will have advantage compared to the one that had the similar amount of bets on bigger odds.
You are only taking into the account the starting balance and end balance which is wrong because a player might not actually use the whole starting capital to obtain that profit.
It is general consensus among sports bettors that Yield is the way to go when calculating someones profitability.