How much of your bankroll should be live
How much money should be on the table at one time?
Two different questions get confused here. How much should one bet be, and how much should be on the table at once. The second has almost no coverage anywhere, and it is the one that ends bankrolls.
One bet
Cap it at 5% of bankroll regardless of what Kelly says. Kelly on a genuine 30% edge and on a stale line ask for the same stake, and the cap is what makes the difference between them survivable.
Everything at once
Above 25% of bankroll live simultaneously, the question stops being about any single bet. On a 20,000 bankroll that is money you cannot re-deploy, cannot re-price, and cannot hedge if the correlation you did not measure turns out to be higher than you assumed.
And the single-bet cap has to shrink as the book fills. Holding eleven correlated bets, the 1,000.00 that was right on an empty book becomes 409.96.
Why this is not conservatism
For genuinely independent simultaneous bets, the individual optima are still right and shrinking them would be superstition — the easy way to look prudent while being wrong. The shrink is a response to measured correlation and nothing else. At ρ = 0 the factor is exactly 1.0 and every bet stays full size.