WP DW Water Feed To Top Wash Arm
The center tower system has less problems, but the rear direct-feed works about as well.
The little bits of plastic you found in the WA nozzles was careless loading that allowed plastic trash to get into the DW. This is a major problem for some users, it seems that we see it most often in Maytag standard tub DWs, I guess because their arms have such small holes to catch the plastic bits.
John L.