Yes, I know, this is frequently asked. Edge loops and creases solve most issues with this modifier. My problem, though, I can't seem to find anything on. I want the corners within this open rectangle to be sharp. According to blender's online manual (v2.79 is what I'm looking at), it's something to do with concave Ngons (which I know nothing about). Also, this is for 3D printing (hence the solidify modifier) if that opens or closes any options.
I know that my topology isn't the most even, I intend to fix that right after posting this. I have tried adding vertices and moving them towards the corners, as I have done in this section:
But that doesn't give me desirable results (plus messy topology to get it to look even halfway decent), and it's even worse in the area I'm trying to fix currently.
Any ideas? I apologize if there is a similar question that I'm just failing to find. Thanks in advance