Depth of field always decreases when focal length increases, I shoot alot with big glass on 35 when doing wildlife work and the longer the lens the shorter the DOF which requires much more precise focusing, but the DOF between a 80 and a 100 is going to be very little. And the 100 you got on your 1000s was not the standard kit lens, the 1000s came with the 80 as well.

Dave