Right...
Take a look at this skived copper block (from
this review):
I know it's hard to tell, but the fins are shaved from the baseplate.
As for the ratio, If you plan on having channels that are 0.8 mm wide, and fins that are 0.2mm thick, then your channel-to-fin ratio is 4:1
So for a ratio of 8:1, with 0.2mm thick fins, your channel would be 1.6mm.