Service Operations - Fetch 1 vs. Fetch Many

Has anyone any experience in how we should construct our implementation for a Domain when we want to retrieve multiple records instead of individual records.

This is for scenarios where we need to fetch data from the mainframe and the bank wants to avoid making too many calls to the mainframe due to cost.

The service domain we are using for this use case is Current Account. We have a scenario were an end user wants to get the balances for their accounts but may also be an owner/administrator for other account. For example they may have visibility of their childrens accounts or a school sports account.

When we make a call to the Party Reference Data Dictionary we retrieve the user and any associated entities. We could loop through this array of users and retrieve the balances for each account from the Service Domain however to optimise this we would want to make a single call to retrieve all accounts and their details.

The current account service domain has the following base urls

Open

Would you recommend adding a new behaviour qualifier for associated entities or creating another Retrieve but passing an array of account identifiers?

Has anybody implemented this or similar pattern?