In control line the fuel is always forced to the outside of the circle. That's why many control line tanks are triangular and they don't need a clunk. The fuel goes to that outside angle dependably. There are exceptions, of course, such as control line combat where the planes are flown violently. They tend to use bladder tanks. I'm not sure if this is the primary reason, but a bladder tank will always pick up fuel until the fuel is gone or the engine quits because there is no air ever in the bladder.

And I absolutely agree with JohnBuckner on the bung hole. A tank stuffed tightly into a hole in the firewall is getting a lot of vibration. I always completely wrap my tanks in latex foam rubber and never let any side of the tank touch structure. And I never have fuel-feed issues.