Can anyone tell me how to set up a cake with columns and a fountain under it? I have an off brand fountain with the same dimensions as Wilton's which says to use a 14 inch or larger separater plate. I am using a 16 inch but there is no room for the fountain under it if you put the four 13 inch pillars in the feet of the separater plate. Am I missing something?

It sounds like the pillars are not tall enough. In the past for cakes that I made using pillars with fountains, the pillars were at least 13 3/4 inches or taller. Recheck you pillar heights. I have used fountains that were not Wiltons. Sometimes I had to remove the top tier of the fountain to limit the height of the fountain so it could be used. HTH and Best Wishes
Hammy