I don't think it should make a soft close sound when dropped the last six inches.

By the time you have closed the hatch that much, the gas-struts are at an extremely disadvantageous angle.

Even if they exerted a linear force several times what they do, by the time you close the hatch that much their mounting geometry is such that they can't push very hard in a direction that supplies a meaningful moment to resist the moment (torque from the weight of the hatch trying to rotate about the hinge) created by gravity.