PETG-HF Stacking with PLA - Work in Progress

THIS IS A WORK IN PROGRESS There's a little bit out there about stacking prints but from what I've found so far it is mostly stacking PLA prints with a PETG interface and it hasn't seemed to work well for me. I have a specific use case for this with a model that has parallel flat surfaces and a decent surface area plus I need to have those surfaces come out reasonably well as I sell these. If I could stack them I could get more on my build plate. This model includes like size box shapes (10x20x20mm) that are stacked on top of each other. I then put a same sized (in X/Y dimensions) cube in between them that is 1mm tall. The lower cube sits on the build plate at 0. The PLA interface sits at 20.18 mm, so just floating above the lower cube. And finally, the top cube is at 21.2, again, just floating above the PLA interface. The settings are primarily the defaults. I'm using PETG-HF and PLA-Basic, default settings for those. Globally I have set the infill for Cubic. For the P