Nothing should touch the z, that makes it even worse. Anchor everything to the gantry. touching the top of the z is like a torque wrench on the bit. I understand what you are saying about the dust stuff but there is no reason to have a rigid tube there. Mount the hose directly to the bottom of the shoe and anchor it to the gantry. You will be surprised how it helps. I don’t use a dust shoe because I value my accuracy over my time (for now).