And if that doesn't do it, ensure that the clunk doesn't hit the rear of the tank when
swinging through from upright to inverted. It should clear it by 1/16"-1/8" to be safe.

You might actually remove the tank and put it at every conceivable angle, to make double
sure it doesn't hit or hang at any point. It has to be freely mobile to fly wild and crazy

Edit... note that this is generally more of a problem on "squared off" tank designs.