Ken,
My experience - 1/2A tanks are short, flex tubing in tank needs all the length you can incorporate to allow full motion. If too short it wont flex as much as you want. I have found the provided flex is a little too stiff for the small tanks and doesnot allow full travel. To help minimize this:
Minimize the fuel feed brass tubing length in the tank to allow longer run of flex line.
On the Sullivan slant tank, bend the brass tube slightly, inside the tank, so it allows a straight run of the flex line to the rear of the tank.
Ensure the clunk weight has clearance from rear of tank so it doesnot hang up.
Bias the clunk motion slightly outboard.
I now use a 2 oz. cylindrical, more length/more "flex" in the tank.
This works for me.
Roger 

Thanks Larry, good tip!
Roger