I haven't been able to grab the tile out of the game yet, but I did extract this from a RAM dump. Looks like the portraits are compressed on-disc and in RAM, and only decompressed into the VDP RAM when displayed. https://awoo.space/media/5C_Yz7zQczabpsiNueA
I have a decent guess what the compression scheme is, but it's not playing as nicely with me as Lunar's compression is. Maybe my guess is wrong.