Just thought i'd give you my views on this topic
I've kept gold fish for close to 4 years now and have common goldfish along with black moores, comets and veiltails.
Now i found that comets are bullies and chase others, i also found that my bigger common goldfish also chased after the veiltails, and kept fin nipping.
So i decided to take my veiltail out of the bullies playground, and put him in with a black moore i just bought (because blackmoores don't like to be on their own).
Over time, i decided to keep them seperate, and have one tank for fish such as comets and commons, and one for more fancy tailed fish, such as fantail and blackmoores.
So in my opinon keeping your commons with your veiltail's is unfair on the veils, seem as though it seems that you're common is bullying and being aggressive towards it, and will eventually lead to damaged fins.