Apokolips is bigger due to it being on a different plane of existence but 99% of the time when someone enters the New God's dimension, they are the same size. Unless someone specifies that it's the New God dimension Darkseid and a being from the regular Universe, it doesn't matter. Meaning, using Darkseid moving Apokolips and then trying to make it more impressive due to the scale New Gods operate on won't fly. Not in claims of superiority. Just like claiming Superman survived two incredibly large planets colliding instead of two regular Earth sized planets makes him superior to another peer. It doesn't matter. If someone is comparable to Superman durability wise or Darkseid psionic energy wise, when moved to the New God dimension, they'll perform the same feats.
Not sure if I explained myself very well.