Well, first off, it's not the best of setups.

Let's do a little "Tank 101" here. The reason you want to keep the tank close to the engine is so the engine doesn't have to draw fuel from a long distance. This is not so bad when you're plane is level, but when it's nose-up it's having to lift a long column of fuel up through the fuel line.

So in your case, the header tank is doing virtually nothing - You should even consider removing it.

You see, even though it is close to the engine, and the engine is drawing from it, IT is drawing from the main tank. So in esscense, the engine is drawing from the main tank. In other words, imagine having a long line directly from the engine to the main tank and then having a large bulge in that line just behind the engine. That is basically what your header tank is. (I'm working on a computer without Photoshop or I'd draw a picture).

What this boilds down to is: If your engine runs fine with the tank back at the CG, you might as well pitch the header tank as it is only complicating things.

As to your fill problem, check the lines inside the tank, sounds like something is plugged