I don't know that I would classify it as aggressive versus non-agressive, but certainly passive versus active. Many of the other Phoenix Sorcerer abilities I crafted are passive in nature in that they only activate once certain conditions have been met. In my personal opinion, abilities that rely to a greater extent on DM fiat or chance should be greater in power or scope since the control is not in the hands of the player. That can be done by either making those individual powers greater, or by boosting other abilities. I see Mantle of Flame in this way. It is boosted a bit more to provide balance to the higher level abilities that the player won't always see use of.Aggressive powers like Mantle of Flame need a much more careful watch than non-aggressive powers like Darkvision.
As an example, a champion's increased crit range is aggressive, but also passive. The player has no control over when or how often they crit. Thus if a player never crits, then that can impact the player's enjoyment of the class. As a result, in my games I balance this by also house ruling that champions also get a +1 damage boost when hitting with a weapon. This is also aggressive, but passive, yet it happens much more often and thus can raise a player's enjoyment even if they don't crit very frequently.