What determines which column of an array that is the RowSource of a listbox is linked to the incremental search functionality?

I have a listbox based on an array with 4 columns (Id, Company, Lastname, Firstname. The control is Bound To column 1. The array is produced by a SQL Select where the Order is on "Lastname,Firstname."

No matter what I do, the incremental search finds the next first name, whereas I want it to find the next Lastname.

Does the BoundTo prop. have anything to do with it?

TIA

Jim