There is no universally valid or correct design of the IR function. Companies are free to find the solution that is right for them.
IR is a synonym for communication with the capital market and in this respect a production factor to help a company secure and procure the resource that is capital as cost-effectively as possible. This premise helps in the budgeting process.
If a company is compelled to use or to change their IR consultant, it is advisable to get suggestions for possible partners from market experts, investors, analysts, and similar companies.
Here’s a piece of management wisdom taken from Toyota that is also apt for the IR function: «Be strict with the process but soft with the employees.»