Where is that quote from?
It seems to me that the only way to hit the 90% target would be to include 270kg of dead-weight tungsten, and fit all the science into a 30kg budget.
It seems to me that the only way to hit the 90% target would be to include 270kg of dead-weight tungsten, and fit all the science into a 30kg budget.
EDIT: To your second point: Even though it's 300 kg total, it looks like that's allocated to 2 75 kg objects and 6 25 kg objects. I would assume that means much less weight/space per unit to work with, given the dead weight to go along with it.