I am wondering about the different front uprights for the mtx4?

I have the TO138-b and TO164 which is the 2 degree upright.
I believe that the original ones are TO138.
My question is, if the TO138-B uprights were to fix the bump steer issue, are the new TO164 uprights to make it even better or is there a different reason for the 2 Degrees upright?
Cheers
Joe