Cats throwing up

I live with 6 kitties. I keep 2 feeders full of dry food 24/7 - one upstairs and one down. At dinner time they each get about 1/4 cup canned food mixed with a little water.

Most days I will find vomited dry food - sometimes more than one pile.

Everyone is healthy,, so my theory is that there is too much "competition" for food, so they eat too fast and then it comes back up.  The competition is not real. There is plenty for everyone. 

I've been thinking of adding 2 more feeders. Probably alongside the current ones.

To others in a multi-cat household, have you experienced something similar?

One or more may have developed an allergy to the food. My ragdoll is perfectly healthy but will throw up with certain foods.

I think it's important to try and find out if this is one particular cat who's throwing up a lot, or if it's various cats randomly throwing up.
If the feeders are out all the time, I wouldn't think there's much competition then. Is one cat more dominant? Perhaps making another feel nervous when eating?