"E" wrote to say he was really surprised to discover that his sweet potato tubers weren't right under the plant like it is with Irish potatoes. For most sweet potato varieties, he's right. First of all, sweet potatoes and Irish potatoes are two totally different crops. They aren't related. So I wouldn't compare them.
There are indeed some sweet potato varieties that will grow most of their tubers right under the mother plant. But I'm finding that most varieties do not. In fact, I have one variety that produces tubers several feet away from the mother plant, making it challenging to harvest them. Truthfully, I don't even try. I just use the greenery as livestock fodder. Occasionally I'll happen upon a tuber or two.
But I've found some varieties can be quite variable. In the photos below, I pulled out some young plants in order to open a space to plant a moringa seedling. These 3 plants nicely demonstrate the variation I find I this variety. (photos taken on the tailgate of my pickup truck.)
Plant #1.... No start of tuber development yet. With this variety it is not uncommon to find a percentage of plants with zero tubers. This particular plant is just a baby, so it would have had plenty of time still to produce tubers, if it were so inclined.
Plant #2..... Very young tuber starting close to the base of the plant.