I've made a form that has different sections that will be visible/hidden depending on which boxes and buttons are selected. Both the pages and subforms within in the pages are set to Flowed. Whenever I hide a section on a page (say, the upper section), the bottom sections move up into the white space. My problem is, when I hide a section on the bottom of a page, the subsequent pages do not flow upwards to fill the empty space. Therefore, I am left with lots of empty white space throughout my form (6 pages), instead of the entire form expanding and collapsing to accommodate subforms.
I also have the "allow page breaks" check box checked on all my pages and subforms.
In your Hierarchy, make sure all of your subforms are included in the parent page 1 subform (by default this is named "(untitled Subform) (page 1)"). If the subforms you've built are within separate 'page' subforms, they will not flow upward how you want.
Typically, I start building lengthy forms with everything 'positioned' and on as many separate pages as I need, then when I'm finished I set applicable subforms to 'flowed' and move them all up into the parent page 1 subform.