Hi Gana,
I know this is 3 years ago that you asked this question, however it could be a live one with others. I myself are searching for a guide on how to setup the dummy pg, but to answer your question.
Side A sees 5 PG's (from both sides). Side A will go active when it sees 50% or more PG's. In this scenario, Side A will be active when seeing 3 PG's. If the WAN link goes down, it will only see 2 PG's and will NOT be active.
Side A sees 5 PG's as well. Side B will go active when it sees more than 50%. In this scenario, Side B will be active when seeing 3 PG's. If the WAN link goes down, it will only see 3 PG's and will be active.
Hope this clarifies your question you had a long time ago.