Steps/mm for dual z config

Dual Z in series steps/mm.
I am just getting setup with duet, but this is not making sense
I set the following up to get the Z platform moving
M350 X16 Y16 Z16 E16:16 I1 ; Set 16x microstepping with interpolation
M574 X1 Y1 Z0 S1 ; set endstop configuration (X and Y endstops only, at low end, active high)
M906 X800 Y800 Z2800 E1000 ; Set motor currents (mA)
M201 X800 Y800 Z15 E1000 ; Accelerations (mm/s^2)
M203 X15000 Y15000 Z500 E3600 ; Maximum speeds (mm/min)
M566 X600 Y600 Z30 E20 ; Minimum speeds mm/minute
M208 X600 Y600 Z600 ; set axis maxima (adjust to suit your machine)
M208 X0 Y0 Z0.2 S1 ; set axis minimum (adjust to make X=0 and Y=0 the edge of the bed)
M92 X80 Y80 Z400 ; Set axis steps/mmThis gets it to move the correct amount, but it's wrong by calculating the step per mm. I'm using 2 nema 23s 2.8a steppers. They're 200 step and 2mm pitch lead screw
So 200/2 = 100 * 16 = 1600. So Z steps/mm should be 1600, but when I did that it moved 4 times the amount. This is really bugging me, what am I doing wrong.I plan on doubling up Y as well and wiring those in series also because I will be using all 11 stepper drivers when all said and done, so is this a series stepper thing or am I missing something?

Figured it out the lead screws are Tr8*82p (4 starts) – so 8mm pitch in reality, so 400 steps/mm makes sense.