How to stop Sales Order Shipping Instruction defaulting to order line

Summary:

Current all order header shipping instructions are defaulted also to all line level shipping instruction. What is the correct method to suppress

Content (please ensure you mask any confidential information):

We would expect a shipping instruction can be set at order header, then allow user to add unique line level against a specific order line. This data for us is transposed to internal pick slips.

While the header is defaulted to the line, the pick slip has repeated text and confusing for warehouse user.

We have been told this is standard behaviour and wish to learn how to stop it.