As an independent, paid hourly, On many gigs over the years I have tried to to get 4 day (28 or 32 hrs) work weeks, but most client companies still insist on a 40 hour week. I work mostly in the northern midwest for mostly large enterprises, and these clients are "conservative", and 40 hours is "what is needed". I don't try to bill fewer hours at a higher rate.

The way OP was using 4/4 was to mean 4 days per week, 4 hours per day. So 4/5 would be 50% of the hours for 80% of the pay.