Oops, didn't see that the previous try at this post actually posted:)

The corresponding database field stores the products_options_sort_order value, but I'm not sure where the PRODUCTS_OPTIONS_SORT_ORDER constant's value is set. It is not defined in a PHP file, so it must be set in admin and stored in the db, then retrieved at runtime. I've never been able to find out how/where stored settings are turned into constants for use.