Ender 5 plus stepper , steps per mm

Slowly setting my Ender 5 plus for the duetwifi , But having problem with the z axis.
Made all my homing files and working correct .
I home X and Y and tell it to go to X175 , Y175 and do a G30 in the middle of the bed.
All spot on , now drop down the bed 100mm and only getting about 50mm drop !!!!
Tried boosting the current to 1400ma and still get the same result .
Is the Ender 5 plus 200 steps per mm or is it missing half of it's steps ?
I may have to connect back the control board and ask it what the step per mm was !! 
@peter247 Assuming you are using 16X microstepping and 1.8 degree motors, then 200 steps per mm would translate to a lead of 16mm which is highly unlikely. I would imagine that the screws are more likely to be 2mm pitch, 4 start giving a lead of 8mm which would need 400 steps per mm.

@deckingman I went the wrong way !!!! I halfling the steps per mm I should have doubled it and said 800 steps per mm .
Like you would have gone with 400 steps per mm which is the default.
BUT , I've been looking at the marlin source and it says under Ender 5 !!!.// If you have the new Ender 5 or Ender 5 Pro Model that has the new 800steps/mm Z leadscrew uncomment the below option to set the correct steps/mm
#define ENDER5_NEW_LEADSCREW. 
@peter247 You need to know the lead of the screws and the step angle of the motor, then you can calculate the correct steps per mm to use. I don't have that information so I can only make guesses.
If the step angle of the motor is 1.8 degrees, then one rotation is 200 full steps. This is where you need to know the lead of the screw so that you can calculate how far 1 full step will move a nut on the screw. So for example if the lead is 8mm, then 200 full steps = 8 mm so 1 mm must be 200/8 full steps = 25. Multiple this by the microstepping (usually 16x) and you get 400 steps per mm. If the lead was 4mm then you get 200/4 = 50 full steps perm x 16 = 800. Or if you use 0.9 degree motors, then the number of full steps per revolution is 400 instead of 200. etc...

I think Creality switched to a shallower angle lead screw with the newer Ender 5s to reduce the tendency for the bed to drop, so 800 is correct.