In the scheduler there are two parameters for this, one for each side of the opening. (This is to account for situations using a "reveal".) They are:
W/D opening height on the reveal side
W/D opening height on the side opposite to the reveal side
When the reveal is not used these values will be the same. I'm not sure where the term "reveal" comes from as I believe it is called a "rebate" in the UK, and nothing (AFAIK) here in the US since our ROs are pretty much all straight through.
I had all my doors set with invisible reveals, that I didn't actually want, and these were throwing those header values all over the map. Once I corrected all doors to have "No Reveal" everything is looking cherry and those header parameters you described read fine now.
There are 3 types of opening size available for listing; wallhole, reveal and unit dimensions.
Edit the scheme settings, go to the 'Additional Parameters' button at the bottom, then navigate to the window/door of choice in the library. In the list of available parameters look for ac_wallhole_width, ac_reveal_width & ac_unit_width.
The wallhole dimensions should display what you need.
What happened is I got thrown off by having all my doors set with "reveal" bevels, and this was throwing off the wallhole sizes. Once I switched back to the "no reveal" option for all doors/windows, everything made sense again.