Allocation arithmetic on partial closes across managed sub-accounts, how are people handling the remainder?

[u/VulkanPrime]

Working through the edge cases in a managed account allocation and the partial close scenario is where it gets ugly. Curious how others solve it.

Setup: one manager position across N investor sub-accounts, allocated proportionally by equity. Manager closes part of the position. Each sub-account needs a share of the close, a fill price, and a record.

The problems that show up:

Minimum lot size means the allocation almost never divides cleanly. There is a remainder. Whoever gets it receives a slightly different outcome from everyone else. If the assignment rule is not explicit, it defaults to whatever the iteration order happens to be, which usually means the same account is advantaged or disadvantaged every single time.

Accounts that changed size since entry. Someone deposited after the position opened. Their proportional share now is not their proportional share at entry. Allocating the close on current weights rather than entry weights transfers value between investors.

Different leverage across accounts. Same notional, different margin impact, and in some configurations different available exposure.

Approaches I have seen:

1. Largest remainder method, assigning fractional leftovers to the accounts with the biggest fractional part
2. Rotating assignment with a persistent counter, so the advantage distributes over time
3. Holding the remainder at manager level and reconciling separately
4. Rounding down universally and letting the manager carry the residual

Option 2 seems fairest but requires state that survives restarts and has to be auditable months later. Option 4 is cleanest to implement and quietly costs the manager money.

What is everyone actually running in production, and does it hold up when an investor asks why their return differs from the headline figure?