Your yield is excellent. Milky whey can be from a poor set, but it also comes from being too aggressive with the cutting and stirring. Try letting your curds heal longer. On Mozz for example, I cut vertically in 1 direction only, rest for 5 minutes, then finish the vertical in the perpendicular direction, rest 5 minutes, then do the horizontal cuts. Stir gently, especially when the curds are more fragile than normal.
There are 2 different important proteins in milk - casein (calcium) and albumin. When making cheese, we primarily coagulate the casein and the albumin is left in the whey. That's where Ricotta comes from.