Thanks - got me into the right area. The "rough opening" setting actually resolved the issue from a visual perspective.
I didn't notice the framing being adjusted though even after I rebuilt the wall framing. I tried adjusting the cutout value too but I guess this isn't a poured concrete wall and that could be the reason why it didn't appear to make any difference.
BigAl123's post in Doorway spanning a pony wall won't trim out the concrete block on lower half. was marked as the answer