Valvetrain complete, but a few ???'s

Don't know if they can help me. I'm a dealer and have installed several of these kits with no issues. This is the first one that is mounted ABOVE the stock oil filter mount. I incorporated an incline in the hose to mitigate drainback, but apparently the little bit of oil that IS draining back is enough to cause an absence of oil pressure (for about 2 seconds).