So I've just sorted my duff maths in first post ! And it proves I can't make tea and post at the same time , anyways the manual gives an example of a servo :
Motor rotates one cycle every 5000 pulses and tool moves 10mm
CMR/CMD = 5000/(10x1000) = 1/2
CMR : Gear ratio numerator
CMD : Gear rato denominator

I'm running at 1/3 which gives me the 3mm over run , if your right and I need to put in 1600/5 then that would be great as I wouldn't have to frazzle my brain with maths. They just look big numbers compared to the manual and I never thought about it that way . Il try tomorrow see what happens .... Can't be that easy , it's Chinese !
Thanks