Just guessing that the angle is for the same or similar situation that the arm I showed was for... compensation for the differential seen when one servo is controlling the ailerons. Just a guess still.
It's hard to guess at which arm to use from just a pic... I'd pick the one that feels the strongest. I'd also be worried that the servo isn't as strong as the two you had shown in the previous pick... so check their specs vs the other servo's and make sure they have at least twice the power of each of the other ones.