Hmmm, maybe change out that dark side tire. [emoji56]
Just kidding of course. I thought that was just a N/O switch - on or off. I totally don't get it acting like a variable voltage. Disconnect the switch and jumper the connector to see if it acts normal. Process of elimination in the absence of any experience from our esteemed brethren.
It could also be the switch is not making good contact at the beginning of travel (wear). Replacing it with a new unit should fix that problem. You might also douse the switch assembly with WD-40 to clean the contact surfaces and see if it improves the behavior.