Hi,
The switching system of the variants only support one switching for the custom product fields area. It wasn't meant to support what you want.
So in that case, you would have to cheat and use the ids of other elements which can switch like the description, the product code, etc. And the modifications for the separation of the fields will be much more complex as it needs to be done in the show_tabular (for the main areas) and in the "show" view files (for the variants custom product field data).