i have always believed a prefilter to be something of a mechanical filter, to catch large particles, and remove them from circulating through the tank before any other filteration is done, and usually the best mechanical filter is filter floss and if it is kept fairly clean there is little disturbance to the flow rate from my experience at least.
it was my idea brent wanted a combo refuge/sump so you would want to put chemical and mechanical in place where it will get the highest flow of water, and since he wants a refuge it would make sense to do both chemical and mechanical before the refuge. Since he wanted a refuge to begin with, i would suggest putting the lr
there, where it will get the most contact time with water.
but your probably right, we have slightly different definitions of a prefilter.