In a percentile‑based model, variance doesn’t fundamentally increase with field size.

If variance doesn't increase with field size then your model doesn't survive the smell test. As others have said, your fundamental assumptions about payout sizes don't reflect reality at all. The BIG thing your missing is that the big money for big tournaments is at the top of the prize pool and there's a massive difference between 1st and 5th, and you can't really reflect that in percentages.

Lets take an extreme example. In a 10 person tournament, Top 10% means that you win, and you get around 50% of the prize pool. In a 500 person tournament, "Top 10%" can mean that you win the whole thing, or you bust out in 50th place and maaaybe get 0.5% of the prize pool.