I think of most “Landing Pages” as “Header Information”. So, in this case, Order Entry Landing Page provides information you find on the Sales Order Header (which includes the SalesRepList). The PartNum is a level down in OrderDtl. So it wouldn’t inherently show at the header level.
One thing you can do is create a BAQ which includes both OrderHed and OrderDtl information, then customize the landing page with a new BAQ grid instead of the standard grid to show the new results.
I did this for our Opportunity/Quotes landing page and it has worked well…
But… just know that you may have repeating data. You’ll get a row for each Line Item… not just (1) for each Sales Order.
You COULD, potentially, create a calculated field in your BAQ that concatenates all sales order line items into a single string (list). That could get you back to one line per order in the final grid.