1 sat = 1 sat! :D The fees are in ppm. So, for an 1M channel you get (1e6 * f_ppm + n * f_base) in fees (ish - excluding reserves etc.), regardless of the fiat price of bitcoin (n is the tx count). If f_base is zero then the count of transactions doesn't matter unless you're on an edge and can do rounding to your benefit. So, you earn more in fiat terms but not in sat terms.