I’m pretty sure this means net successes. My interpretation is that your final Ob in a Vs Test is your opponent’s successes minus their Ob penalty, plus your Ob penalty. (I usually set a floor on this to 1 for advancement, but I think that’s a drift; I think RAW, the floor is 0, which you don’t get to log. I’m not sure, though.)
In our example, we change the variable to +4 Ob. The Wizard increases the number of successes he needs to win by 4.
Here’s some of Thor’s commentary from that thread you linked in your first post:
Thor is wise.
I recommend checking out the rest of that post for his commentary on Skilled Vs Unskilled.
EDIT:
You’re welcome, man! I’m always game for talkin’ Burning Wheel!