Fleck 5600sxt brine fill and draw

After years of struggling with an old AquaSoft, I installed a Fleck 5600sxt. All went smoothly re install (Sharkbite rules!) and programming except the brine draw cycle. All online recommendations say 60 minutes but that would be about 25 gallons when all I need is about 5 gallons. I can set the brine draw and the brine fill to match up but I think I'm missing something. If the brine draw exceeds the fill, then the system just sucks air. I don't have a brine tank float valve but I though tat was just to prevent overflow. Perhaps the system should suck air so that the brine solution stays in the resin tank for awhile!? What gives?