Your system may be under filled causing too much lever stroke to activate the brakes. When you fill/bleed you have to make sure the lever reach is adjusted properly, See the video below at about 3:28. Another thing to try is removing the wheel and gently pressing the brake to extend the pads. If they rub the disc push them back in a little. The idea is to get the pads as far out as you can without rubbing. That way the lever doesn’t need to move as far when braking.
It’s essentially like a pad contact adjustment.
