On the other hand, is one "unit" of student effort equivalent to one unit of staff scientist work? I would say no: early-PhD students in particular are still l

On the other hand, is one "unit" of student effort equivalent to one unit of staff scientist work? I would say no: early-PhD students in particular are still learning and have other responsibilities (coursework, quals, etc) to boot. You can also interpret your numbers as suggesting that an experienced person is 2-3x more productive than a trainee, which seems....quite reasonable, actually. I think that's the other "secret": the combination of large budgets and tight timelines encourage the use of more experienced staff and smarter division of labor: hire a programmer for this, contract out to a machinist for that. This is very different from the model used on most NIH grants, where grad students are used as jack-of-all-trades.