Heroic Realm

[Revan]

Yes, the boss I am on has gained about 20M power. I assume it is only for bosses above a certain power level (a power where the player fighting the boss is expected to have the 6th slot open) in order to keep people from advancing too fast with their new hero in a lineup of 6.

They have added power to all of them yes.
You can confirm this by looking at the replays.

They have all indeed gained power of varying amounts, there seems to not be exact ratio that can be applied to all of the bosses.