What option allows you to add a custom col field to the expense sublist on a bill? It's appearing on the Item side.

I believe its the checkbox on the definition of the column itself

Expense

I have all that checked. I tried to look at another field that appears on both expenses and items, but for some reason it's only appearing on the Item side.

I assume you checked the definition of the form itself, right?

Yea. Under Sublist Fields I checked the option to show the field and now it shows on the item side. There is nothing here differentiating expense vs item though. I see one field that is on the expense side, but not the item side