Ok, after some trial and error, I seemingly solved my own issue.
If I take the horizontal width of my viewport in my template then divide that by two to get half, that distance establishes the horizontal centerline or middle of my viewport. If I enter this distance in the Vertical major: box of the Plot Area tab on the Group Plot Style editor, the process places my section views centered within the viewport.
The result is exactly what I was looking for.
Hope this is helpful.