(Help) Trying to create pixel perfect hard-edged brushes

Hi there! I'm new to Adobe Capture. I downloaded the software on my iPad after hearing about its function of using images to create brushes for Photoshop and Fresco. I was planning to use that feature to create a specific type of halftone brush(es). The first brush I made was super easy and worked fine, it was only one pixel wide and black in color. I made the image on a different app with a pixel art feature, then imported it into Capture. When I tried to make my next brush, something odd happened. I made a brush that was 2 by 2 pixels, with only 2 of those 4 pixels being colored in with black. The image automatically blurs when I try to make it into a brush. I tried upscaling it, same problem. I would like this brush to only show up in color in the black spots. Does anyone know how I could go about doing that? Do I need to make the transparent spots of the aforementioned brush white instead of alpha?