Standard deviation, which is what you guys mean when you say variance, is sqrt(%1(W1-a)^2+%2(W2-a)+%3(W3-a)+%4(BI-a)), where %1 is chance to come in 1st, W1 is money earned for first, a is expected win, %4 is odds of losing, and BI is the buy-in. So, it's certainly affected by your ROI and your place distrubution, not just the payout structure, and how it changes relative to those depends on what they are specifically. For a player with a 20% ROI or so, variance increases as ROI goes down because the terms (W1-a)^2, (W2-a)^2, and (W3-a)^2 increase much faster than the terms that decrease.