I hope I understand your question fully, so I will try to answer. Seam fat is the fat deposited between muscle groups, such as what you see in a chuck roast or a blade steak.
Additional seam fat does nothing to influence the marbling score, which is the level of intramuscular fat that the grader uses to assign a quality grade to the carcass. To me, you must achieve a "threshold level" of seam fat to optimize your marbling, but, any external fat over .4" gets trimmed, and to a certain extent, excess seam fat gets thrown in the trim box too.
So to answer your ?, I think feeding for seam fat is a total waste. Feedlot cattle in my opinion are done at .4 fat over the ribeye, save the corn and move on to the next calf.