It seems that you are actually confused about how Auras work.  

An Aura is active only when the toon with the Aura is the team leader.

If you have a toon with Intimidating Presence on your team (in any position), the highest level of IP on your team will modify the aura of your team leader for that specific fight.  The boost to the aura (and penalty to the opponent's aura) will happen in the background of the fight.  You will not see any visual representation of that.

as wileyman said, but also the 7.5% bonus is multiplicative, not additive. you're adding 7.5% of the initial 30% boost, bringing the overall aura effect to a 32.25% increase. otherwise, it wouldn't work properly for acc/res auras that aren't % based (not to mention how utterly broken intimidating presence would be at 6 stars).

So you will not see it. but it's being added.

still is it worth it, 2.5% do not sound like much.