How many bets are you actually making
Are twelve simultaneous bets really twelve bets?
Twelve bets on one evening's slate are not twelve bets. They share weather, pace, injury news and a referee, and everything they share makes them a smaller number of larger positions than the count suggests.
The arithmetic is exact once you have a correlation. For n bets with
average pairwise correlation ρ, the number of independent bets you are
really holding is n / (1 + (n-1)ρ):
| Positions | At ρ = 0.15 | At ρ = 0.45 |
|---|---|---|
| 2 | 1.7 | 1.4 |
| 4 | 2.8 | 1.7 |
| 8 | 3.9 | 1.9 |
| 12 | 4.5 | 2.0 |
| 20 | 5.2 | 2.1 |
At 0.45, twelve positions are 2.0 independent bets. Doubling them to twenty gets you to 2.1. That is the part worth sitting with: past a handful of correlated bets, adding more stops buying diversification almost entirely, and only adds stake.
What it does to sizing
A single-bet cap of 5% of bankroll is right for someone holding nothing. On a 20,000 bankroll that is 1,000.00. Holding eleven correlated bets already, the same cap should be 409.96 — the difference is the shrink factor the correlation implies, and it is not a rounding adjustment.
Measure it, do not assume it
ρ can be measured from your own settled record: group bets that resolved together, and read the correlation off how much their combined results swing against what independence predicts. It needs 30 settled bets and 20 multi-bet groups before it is worth anything, and below that the honest answer is a labelled prior rather than a number.