Down flow that I use refills the brine tank at the end and then X number of days later it cleans.. x could be 2 days or 10 days.
Most of the time the 18" dia brine tank with a 4" high salt grid will have about 1-2" of water above the grid.
Check the brine flow control .. what is the gpm? .5gpm .25gpm 1.0gpm take that number multiply it by the time for the refill that gives the gallons going to the brine tank.
Then 3lbs of salt per gallon of water for max of 26-27% to get to that one needs 2-3 hours of time for the water and the salt to get to know each other.
With an up flow the brine is getting to the resin at the start and not having to go through 15" of water before it starts to clean the resin... so yes you can use less salt to get close to the same capacity that the down flow would give.