Why Three Per Cent Adds Up
Per round it is negligible, which is exactly the design. What makes a session cost what it does is that the same share is charged again on every round, and rounds arrive quickly. Sixty of them an hour turns a small per-round share into a predictable hourly figure, which is why turnover rather than the edge is the number worth tracking.
It is also why no market choice and no stopping rule rescues a long session. Those change the shape of the results; the hourly cost is set by how much money passes through the board.
The Honest Version of a Plan
Decide what an evening of this is worth to you as entertainment, divide by the edge to get the turnover it supports, then divide by rounds per hour to get a stake. It takes a minute and it is the only calculation here that reliably does what it says.
The stake side of that calculation is worked through on the stake and bankroll page, and every guide is on the home page.