Could a follower's ATM strategy be different from the leader's?

Short answer: no. The follower always ends up following the leader's ATM Strategy — either by copying the leader's exit orders, or by running the same named ATM Strategy locally when ATM Copy is enabled. Keeping the same strategy is what keeps the follower in sync with the leader for as long as possible, which would not happen with a different ATM Strategy.

How the follower handles exits

The ATM Copy column in the Follower Accounts table is a per-follower toggle (green means on, grey means off). It decides which of the two modes below that account uses. Because it is per follower, enabling it on one account does not enable it on the others.

Replikanto Follower Accounts table with Sim102, Sim103 and Sim104 turned on; the ATM Copy triangle is green for Sim102 and Sim104 and grey for Sim103

1 = ATM Copy column: one toggle per follower. 2 = green (Sim102, and also Sim104): on, the follower runs its own ATM Strategy of the same name for the exits. 3 = grey (Sim103): off, the follower copies the leader's exit orders.

ATM Copy enabled

Replikanto copies the entry and instructs the follower to run its own ATM Strategy of the same name for the exits, instead of copying the leader's exit orders.
NinjaTrader on the follower places that strategy's stop-loss and profit-target orders with One Cancels the Other (OCO) behavior: when either the profit target or the stop-loss triggers, the remaining order is cancelled automatically.
The split of contracts across targets is done by NinjaTrader, according to the strategy definition — any quantity left over after the distribution goes to the first target.

Leader Sim101 and follower Sim102 charts of ES 12-26, each running its own ATM 1 - 1 strategy with the same target at 6520.25 and the same stop at 6508.25

With ATM Copy on: 1 = the leader Sim101 runs ATM 1 (target 6520.25, stop 6508.25). 2 = NinjaTrader on the follower Sim102 runs its own ATM 1 of the same name, with the same target and stop working as an OCO pair.

ATM Copy disabled

Replikanto copies the leader's exit orders to the follower account, and the leader's ATM Strategy is not run there.
In this mode, Ratio scaling is applied to each target individually. For example, a leader ATM of 1/1/1 with Ratio 3 gives the follower 3/3/3 targets — an even distribution, rather than NinjaTrader's default behavior of allocating leftover contracts to the first target.

Requirements for ATM Copy to work

Same ATM Strategy on every node. The same strategy — same name and same configuration — must be present in the NinjaTrader instances of all nodes involved. This applies to local-network followers and to internet-based Remote Copy, and it is the most common reason ATM Copy does not behave as expected.
Trade from NinjaTrader Desktop. Using the leader's ATM Strategy on the follower accounts is only possible when the trade is placed on the leader account from within NinjaTrader Desktop, using an ATM Strategy, with ATM Copy turned on. When trading outside NinjaTrader Desktop, exit orders are copied from the leader even with ATM Copy enabled, and the ATM Strategy is not applied to the followers.
Custom strategies. Custom ATM strategies can be copied to local followers. To use ATM Copy with remote followers, both the leader and the follower accounts must have the same named ATM strategy.

Limitations to keep in mind

ATM strategies cannot be applied to an open position. If a predefined ATM strategy is added to a position from the Positions tab, Replikanto will not be able to copy that applied strategy to the followers.
Setups can differ, but it is not recommended. While the ATM strategies can be different, it is generally recommended to use the same setup as the leader's strategy — the same number of partial exits and contracts. This is not a requirement, but it is what keeps the accounts aligned.
Ratio and Pre Allocation change the quantities. With those copy methods the quantity used in the ATM Strategy can differ per follower, and NinjaTrader performs the target distribution on each follower's side — so define your target quantities with the followers' actual contract counts in mind.

In short

When using ATM Copy, make sure the same named strategy is available on every machine involved, especially with remote followers. If the ATM Copy feature is not used, the follower accounts copy the leader's exit orders instead of running the leader's ATM strategies.

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