Hi GroGreen,
Customers, Leads, Vendors, Employees & OtherNames are all stored in the Entity table and are therefore, all entities. You’ll also notice tables for Customer, Vendor, Employee & OtherName in the list of tables on your account. These are simply views of the Entity table. These views are designed to show only their respective Entity Types.
Leads are simply customer records. The only difference between a lead and a customer is the IsLeadStatusOnly field. Leads have a value of Yes and customers have a value of No. This field determines whether or not the record should be synced with QuickBooks.
In your case, adding the fields to the Customer view will suffice since both customers and leads can be found in this view. The fields will be available whether the record is a lead or a customer. I hope this helps.
--Audisho