Ambiguous inter-chain attention indices definition

Hello. In the following code of RFD3, I am unsure why query_chain is essentially being set to chain_id[c for c in unique_chains] in each loop iteration, where chain_id is of atom sequence length L. My understanding is that this effectively means that inter-chain attention indices are only determined for the first len(unique_chains) atoms within the first unique chain of each batch element (i.e., duplicate structure).

Is that correct? And if so, why should this logic be preferred over something more intuitive like setting query_chain = c for c in unique_chains, to allow each chain to derive its own inter-chain attention indices?

https://github.com/RosettaCommons/foundry/blob/cee116dc5598d2c0c6087701914c5185aac98b48/models/rfd3/src/rfd3/model/layers/block_utils.py#L293