For UA900 SFO-FRA (yes, hardest to upgrade) expertflyer shows PN=3. I am confused about this. Is UA900 applicable for upgrade for elites on B/M fares?

I am trying to figure out best way to increase chance for upgrade on this difficult flight (May 28). If a B fare gets me instant upgrade to BusinessFirst due to PN>0 I am all over it.

Can anyone confirm this is how it works or am I totally off base?