I can plainly see that you are an engineer. I think you are over thinking fuses in a dc system.
As far as I know every fuse I have put in a car has a rating of amperage and no voltage marking except sometimes a rating of 120v. max So what is it that you are saying? If I put a 120v 10amp glass fuse in my car it will blow at aprox 1 amp? I don't believe it works like that. A fuse melts because the excessive amperage heats up the narrow strip and causes it to melt (blow). 10 amps at 12v is the same 10 amps at 6v, and the same 10 amps at 120v. But I'm not an engineer.

1961 ford f500
1953 3100 five window (https://www.facebook.com/1953-Chevrolet-5-window-1533405913413610/)
1955-2 3200 big window (https://www.facebook.com/Leep3200/)
55yrs as a mechanic and retired. (kind of)