Soft limits work from Machine Zero. So if you haven't got home switches installed and enabled then you will need to "Ref All" before soft limits can work. Then the Soft limit will be from the point you Zeroed at. You need to be careful here because let's say you "Ref All" at some point along the axis travel but you have set the soft limit value to be the length of your full travel then it will crash into the ends because it thinks the soft limit is further away. The soft limits are only safe if you have Home switches fitted and have homed the machine first.