"I would want [Silva] to come down as close to 170 as possible if that was the case."
Key sentence from Firas; as close as possible. This is all just negotiations.
GSP typically weighs in at 170 and fights at 185 lbs. He does not balloon to 190+ as many have suggested.
Silva would likely balloon to 200-205 lbs.
An extra 15-20 lbs is a significant advantage when you are talking about the two best p4p fighters in the world.
GSP's camp will try to minimize that advantage as much as possible.
Silva's camp will try to maximize that advantage as much as possible.