In broker settings, there are three choices for OCO group:
Use native OCO group
Reduce size OCO
Overfill protection
What do each of those mean
A native OCO group sends the OCO setting itself to the broker/exchange IN ADDITION to the orders contained within the OCO group. In this case, when one order gets filled, the other order is cancelled by the broker/exchange.
A simulated OCO group sends only the orders to the broker/exchange while the setting to cancel the order that didn’t get filled remains within the MultiCharts software on your computer. When your platform recognizes one of the orders getting filled, MultiCharts sends out a signal to the broker/exchange to have the other order cancelled.
So this means, for example, if your computer crashes while you have a working OCO order group and your MultiCharts is set up for “simulated OCO’s”, you run the risk of both orders getting filled because your situation causes your software to lose the ability to complete the OCO operation.
A reduce size OCO is where if one order in the OCO group gets partially filled, it will proportionally reduce the order size of the other orders in the group.
Overfill protection is related to this, because in the case of a partial fill on one order in the OCO group, reducing the size of the other orders protects you from, for example, a stop loss or take profit order size being larger than your open position.
It is important to note that supported OCO features and types depends on what a particular data feed is offered.