Yeah illusions only give you a faction adjustment, lets say +500 (This is just a guess). As mentioned above, religion is a factor when determining starting faction. If Iksars dislike Bristlebane, you may have a -300 (Also just a guess) from that. In this scenario, the mask would only be giving you a net +200. That isn't bad, but
https://wiki.project1999.com/Faction scowling has 1000 points within it. I am not sure how close Bristlebane Rogues are to the bottom of scowling by default.
I am assuming you haven't been lowering your Iksar factions in some manner, so that probably isn't an additional factor.