this verifies what we just looked at: the lobe has flattened out on top of the shim.

This is not accidental. By flattening out against the shim, the lobe is preparing to, and is moving, the point of contact outward, towards the tip of the lobe.

This is the key to the advantage of a mushroom tappet. By moving the point of contact [and therefore the point of PUSH] further away from the camshaft centerline axis, the length of the moment arm for the force vector--to totally mangle Physics terminology-- is made longer. With the contact point farther away from the cam centerline, the same rotation of the cam lobe causes a farther movement of the shim/tappet. The tappet and the valve move farther for the same amount of camshaft rotation than if the point of contact were closer in.

The next image shows this...