Again smaller wash arms or not have no problems with cleaning performace in my 18" DW. Find the center tower uppper spray more than does the job.
Then again one mainly uses the upper rack for glassware, saucers and maybe small bowls. Anything requiring heavy duty "scubbing" goes on the lower rack.
Probably could place bowls and other more grubby items in the top rack and use either "Pots and Pans" or "Heavy Soil" cycle but we're not on that right now.
Must say however that my DW is >10 years old and uses a decent amount of water which affects cleaning/rinse performance. Unlike these modern DW's that sprinkle dishes with water there is quite abit of force behind my machine's sprays. You can hear it hit the interior top, front and sides of the unit during operation.
I certianly would take an 18" DW over those countertop units sold here as portable units.