Custom structure generating exclusively on nether roof

Hello! I'm somewhat new to datapacks, though I have a lot of programming experience and am good at using commands. I'm trying to create a custom structure - it's a TNT trap that's meant to sit flush with the ground. While making the nether variants, I'm finding that every single time it generates, it goes on the nether roof. I saw a previous post about this problem but their solution was to switch to rigid projection, which I'm already using. Any help is appreciated, as well as any explanation of why this is happening! :D