Currently, we require that the matching kernel has smaller dimensions than the PSF.
There's a tradeoff between pixels being fit and kernel size. When kernels are too small matched-PSFs look square, but they can't be arbitrarily big. This makes the window of appropriate kernel sizes vary narrow, and in some cases non-existent.
This ticket will pad the PSF before matching and test whether this solves the matching problems observed matching HSC PsfExPsfs.