You are growing dahlias like they were potatoes. Most people who start them in pots just put an inch or two of soil in the pot and then the tuber with eye pointing up. They cover it with soil and that would be about 4 to 6 inches of soil. Advantage to starting in pot is that they will bloom earlier. Sounds like you want them to grow more tubers on the stem as you are covering leaf nodes with soil. I do not see any reason to do it your way. The sprout from the tuber has nodes that form roots and tubers.

Thanks. I was under the impression that they would develop quicker if left uncovered. Untrue?