Biomes Being Such A Pain... Help

Okay so Im creating a datapack which for context has a custom dimension but im using the overworld noise preset for it and having custom biomes inside it but the problem is that my custom structures/features started spawning QUITE naturally on the yk ocean as well coz technically its my 'custom_plains' biome since the whole dimension is that.
So to fix that I used the multinoise instead of fixed biome and yk created lets say two biomes one is "custom_oceans" and other is "custom_plains" BUT NO MATTER WHAT I DO- WHICH EVER PARAMETERS I MOVE OR WHATEVER. THEY NEVER ALLIGN. Like it always looks like as if its mixed together both the biomes. HOW DOES VANILLA CREATE THOSE AMAZINGLY EFFICIENT BOUNDARIES. 😭 I tried but couldnt and there is pretty much nothing on the internet regarding that.
The closest I got was having an obnoxiously large range for an ocean that casually consumes atleast 60-70 blocks on average on the Land-Ocean border before switching to the plains biome. 💀 💀 yeah.. 
HELP. 😭