I took a second look at the wiki article and I found this:
...Stops with dims=1,1,8 have a special feature. They got 4 graphics per direction
Dims 1,1,16. This is similar to the dims=1,1,8 stop above, but it has a second variation. in the picture below they're used to make the platform appear on the opposite site of the track...
So, I think that the maximum stop size is 4 parts. Or I'm wrong? 
Edit: "4 parts" I wanted to say 4 unique graphics per direction