OK! I see what you mean now. The seat post is quite thin and the derailleur hanger is "short" so you have nothing to push the screw against.
Hmm interesting. Though it's not mandatory AFAIK, it brings additional strength and adjustment. I am also planing on using an 105 mechanical groupset on it.
Is the hanger fix by rivets or screws?
In any case let us know what she replied
And nice specialized like colours