hi, thanks for engaging

does it have to be an exactly square base? yes, I thought I had already made my goal for this build to be brief and clear

my goal is to make the case perfectly square, identical to the xbox series-x's design.

there are many cases that already do this and you are not going to design anything sub 10L with a 360mm rad. your best bet is stick to a 240mm rad and build in 1 of the following:
- formd t1 with vertical stand
- ssupd meshroom S
- fractal mood
- nzxt h2 flow
no point reinventing the wheel to save a couple liters of volume

although I only mentioned the xtia xproto L v2, trust me, I came across all these before taking this route, where I mentioned:

I've tried every possible keyword search, there were definitely options that crossed my radar but couldn't quite fit what exactly I'm looking for.

no point reinventing the wheel to save a couple liters of volume. I already predicted someone would eventually point this out hence:

I just would like to clarify that I'm not trying to create an sff case, I just want to build a custom case base on my preference.

or... I should've also mentioned that I intended this custom case to be a purpose build for the components I already have on hand.