Can anyone help me out......

I am in the process of building my roof rack yet my defender is at my local specialist having some work done. In the meantime I would like to get everything ready for a straight forward fit tomorrow, yet without my defender I do not know how wide to set the legs as they are pretty much infinitely adjustable in terms of width. If someone has this rack or anything similar could you provide me with the width that I should set the legs of my rack to?

Many thanks.