I have a coating surface that is 20x24" in size so that I can (and have) coated up to 16x20 paper sheets.
When doing plates or film, I simply use a smaller coating blade which is 4" wide and with an undercut that is the width of the glass + the desired coating height which is usually 5 - 7 mils.
This is shown in the sticky slide show in this forum. I tried to upload some photos, but got a "Security Token Missing" and when I tried to report this problem, I got an "Invalid path specified for message". Not my day.