On a dry sump engine, it is always in the best interest to not overfill. The tank needs room to breath as well. Whenever you use thick oil such as 20/50, you should give it (the oil) a chance to break down a little bit. There can be a huge difference in just 300 to 400 rpms and the level the dry sump tank registers. As long as the pick up area is safely covered at all times, your pretty much good to go. We always run our dry sump tanks at about 60 percent capacity and check them at idle (1200 to 1400 rpms) and we also rev them up a little but to make sure the level doesn't do anything real odd. The necks on some of these tanks doesn't really allow you to see in it, and that is extremely poor from an engineering stand point.
P.S. you never want your pick up to be at the very, very bottom of the tank, because that's where sediment and all the garbage drops to. You definitely want your drain plug to be at the bottom though.
As for this post. If it's not leaking and it's not burning it, than it is still in there and your doing something wrong.
When you have to drive them that long to get the proper reading, it only means one thing. That is, the oil pump side is more efficient than the scavenging side of the pump. Poor engineering, it should be visa versa. if you hook a vacuum gauge onto the crankcase, you will most likely have pressure, and that's not good for a dry sump system. It means not matching your charge by the rings with the correct size scavenging lobes. Ultimately there is too much oil swimming in the crankcase when in operation.
You get what you pay for when it comes to dry sump pumps. In the racing world, if your not spending 1800 bucks or greater for an oil pump, than it is most likely junk, and your whole engine design will suffer accordingly. I can almost bet the ranch that the scavenging side on these oil pumps are pure junk! A junked up scavenge side will force oil up the ring package because it's sitting in the crankcase and not in the tank. Vacuum in that crankcase, not pressure, keeps that ring package dry.