The temptation
Funds tend to estimate capacity by extrapolating from average daily volume and a haircut. The number that comes back is, by construction, large enough to fundraise against. It rarely survives a bad week.
How we estimate it
We measure realised slippage on actual fills, weighted by the worst third of execution days. The number that comes back is much smaller than the average-day estimate, but it is the one we plan against.
The rule we keep
We do not raise past the realised number. When demand exceeds it, the queue waits. The rule is unromantic and has cost us money on paper. It has also kept the live track inside the published bands.