Scenario 1 - how it is today - GOOD
You are an approver. You open your invoice and if you create more rows, the new rows are distributed to you automatically
Scenario 2 - how it is today - GOOD
You are a bookkeeper. When you create new rows they are not distributed to you (that would be silly)

Scenario 3 - how it is today - BAD
You are an approver and a bookkeeper. When you work with an invoices that has been sent to you for approval and you create new rows, they are not distributed to you. You have to do it yourself, row by row as you can't do it from the header when row one has already been sent to you

What we want instead
You are an approver and a bookkeeper. You open an invoice that has been sent to you for approval so row one is distributed to the logged in user, who is also a bookkeeper.
You create new rows on this invoice, and they are automatically distributed to you - ie, it works like scenario 1, so long as you are in an invoice that has been sent to you.