TMC2208 drivers - Microsteps configured incorrectly
I don't have these controllers, but I read that with default settings the TMC2208 will interpolate the microsteps set by the I/O configuration pins to
256 microsteps. Please look into how you set up the dip switches / jumper caps on your board, it seems that only 2 are used (MS1 and MS2). Furthermore, can't you just decrease the count of the array  DEFAULT_AXIS_STEPS_PER_UNIT for the Z entry in your configuration file?