The setting represents an average FIX message size that is expected to be received by the session during the lifetime. It is used as a hint for the optimization of the deserialization of large FIX messages with a lot of repeating groups. The large value of the setting can increase the memory consumption by the incoming Message object, so try to increase the value only in case of a latency degradation of the large incoming FIX messages deserialization.

public int ExpectedIncomingMessageSize { get; set; }