Scott; If the flats were for MOW work at Cumbres, it would be logical to place them between the helper and the road engines. That would avoid the necessity of cutting the road engine off of the rest of the train when they were dropped.
Someone with more experience might give us a different opinion, but flat cars between the two engines going up where the helper is pulling should not be a problem. For one thing, because of their shallow vertical section, flats must be built with a pretty heavy cross section and thus are not really a whole lot lighter than the box and other cars in the train.
ElCoke, how about a comment?
Jim