Ok I don't get it, I planted two mango trees. They were both the same size when I planted them. They are 12 feet apart in the same section of yard that get the same light, rain etc, and one is TWICE the size of the other. And the weird thing is, the smaller one is the only one that's ever gotten fruit?
Actually not all Mangos produce fruit at the same time...there are early, early to mid-season, mid-season, mid to late season, late season and one classification called Often Late. Double grafting creates a dwarf tree that produces early and there are some dwarf varieties that have been developed. The nursery where you bought your trees could have left off the info of when in the season they produce and one dwarf could have gotten mis-labeled as well. While they look identical and may have been labeled the same, you could have two different varieties.