I have no clue what possible problem you both see with the shrinking… that’s just a theme, the dlc is a couple of instances. There’s lots of loot we get there, for example all lootbags are “normal” sized, maps are “normal” sized, no matter where you look at them.
In the end the server does not even care in which instance you get an item, it got a unique id which apparently is same in whatever instance, overworld, dungeons or dlc. So a sunfish would show as always on your lure in the dlc (breaking the roleplaying perhaps, granted, but I could not care less…), it goes to your inventory, and if you put it out, for example to craft, it will be like every other sunfish, there’s no change whatsoever.
Any “themed” dlc fish like new models or sizes for minnows etc. would be much more work than just implementing some fishable waters so I don’t have much hope that’s coming.