My understanding of the new v4 forms is that you can only break sections apart by using a separator within a form. Having said that, you could insert a separator for the group with the 3 field below it and then add a blank separator (by clicking insert and selecting the 'Separator Row' but not adding a title and de-selecting collapsible) then add the other 2 items below that separator row and they will be in a separate section surrounded by a thin box.
I am not aware of any way to do it so that you don't use a separator row and not have a box around the items.
Someone please correct me if I am wrong.