You should consider 5 instead of 3. Size of the pendants has a lot to do with it. Is there recessed lighting on the ends of the island? Mini's are usually grouped close together and viewed as 1 lighting elemant. Spreading them out to far, reduces the impact. Work in uneven numbers if you add fixtures. If you stay with 3, try 18" apart with middle one in the middle of the Island. That will leave 24" on either end. If you try to spread 3 out evenly, they will look small and unimportant. We usually keep them 12" apart. Larger pendants can be more evenly spaced over the area. Hope this helps.
Ginger Rushing
Ginger@yourlightsite.com

Ginger,
Thank you for your valued input. I would prefer to place only three as they were costly. Perhaps you know the pendants -Sophia Amber pendants (4.5d x 2.5h). We have not added the recessed yet so we could place the three pendants closer together with recessed can on each end. Little confused though, 12" apart or 18" apart". We have tape hanging for about 20"-22" apart right now. We can easily play with the tape. Can other suggestions? Many thanks