Answer
This is a confirmed, acknowledged architectural limitation of IFS Connect rather than a one-off configuration issue — as a lightweight integration broker, IFS Connect's memory consumption for file processing is disproportionately high (roughly 2GB of heap for every 100MB file processed in-order, multiplied further if messages run in parallel), and IFS R&D has confirmed that properly fixing this requires a future framework redesign rather than a configuration change. Practical mitigations in the meantime: reduce file sizes by sending smaller chunks (requires changes on the sending side), or send files in compressed format (requires changes on both the sending and receiving/processing sides) — simply increasing heap memory is a temporary workaround that will need to be revisited again as file sizes continue to grow.