Setting capacities fixed bin ewm

Hi, I'm new to sap, as the company has just gone over to it, we have had it in since Feb 2013, was using catalyst before that, what I want to know is how is the capacities set for fixed bins, I work on the floor and do not have access to the background, but can pass on the info to those that do.

the way we have found at the moment is to divide the volume of the fix bin by the quantity that will fit, and then change the volume in mat1, we know that binmat sets the replenishment point, but we do not think that changing the volume is the correct way of doing it as changing anything in packspecs will throw all that out.

So I'm hoping someone here can tell me a better way.