I can't speak for the Minimig, but when I bought my A2000 in 1993 it came with Kickstart 1.3 and a 40 meg SCSI HD. It booted right from the HD. Isn't the Minimig designed to be compatible with KS 1.3, even with using the SD/MMC card to IDE?
Yes, the Minimig IS compatible with 1.3.
In fact, that's the KS version I use to boot it when I want it to become an Amiga 500.
But my KS 1.3 is 256KB in size. Maybe it's an 1.3 from A500 wich could be different from a KS 1.3 in an A2000. Just speculating here.