the "set" (number of tubers formed per plant) depends on the variety, possibly other factors as well. The size of the tubers depends on many things including the plant population. So if you had 2 rows side by side with everything identical except population, the higher pop should have smaller tubers.
for reference, commercial potato production is usually either 34 or 36 inch rows and a typical yield is 350-450 hundredweight per acre
so... 40 ft row, assume 36" wide, 35000#/A, 56#/bu, do the math... 1.72 bu.
Yukon Gold isn't known for high yield, and with your home garden I wouldn't expect maximum yields with any crop, so I wouldn't be too upset if there's less.