I would understand it as meaning:
base armor += 5 + man-at-arms*2
So, if man-at-arms is 0, the talent gives you +5 armor.
If man-at-arms is 1, the talent gives you +7 armor.
If man-at-arms is 2, the talent gives you +9 armor.
Haven't checked, but that's my understanding from your post.
Thank you very much rejam! That is it exactly, so yes, a misunderstanding on my part. I appreciate your explanation and you not pointing out my stupidity directly!
