Can you get your rez up higher?
The greater the pressure in the line, the bigger the difference between on and off and the less runoffs. I have run twelve plants on a rez and twelve plants using house pressure water with the step down pressure regulator and the system with the pressure regulator does not runoff at all. Since there is a good deal of pressure in the line, you can tighten down the screw top regulator. When it is off, it is off. It is only when the media starts to get dry that there is a good suction in the carrot that the line opens up enough to let the relatively high pressure water through to wet the media.
Getting your rez up as high as possible gets the pressure in the lines closer to that in systems using the pressure regulator, either using house water pressure or the pump and accumulator method.
Hell, my rez is 12 fucking feet above the blumats It's on the second story and my plants are on the first, ya think I should mount it on the roof 30gal rez on second floor pumps up to a 5 gal bucket, two 1/2" black lines from the bucket go through the floor and circle the bloom room and go back to the bucket. A pump in the 30 gal rez keeps the 5 gal bucket topped off every hour and runs back to the 30 gal thru some 2" abs. I have lots of pressure. When I clean out the lines the pressure is like a garden hose. Maybe I should replace all the carrot tops, they bout 3 years old.