I've been told by the Support team that there is currently no way to control the order of fields on a Service Catalog Request item when using the Form & Text Side-by-side layout.
In my opinion, this makes this view almost worthless, as you can't have any ability to order the fields in any meaningful order. I can reorder the process fields when editing the form, but the live form does not respect any ordering on the actual live form. Making matters even worse, the dependent dropdown fields appear way down the list, making it an extremely confusing process to fill out.
Please make this Service Catalog layout more usable.