The explanatory notes the departments provide are very detailed.
Obviously, senators focus on things that are of interest to them, and those matters of interest are very often politically selected. They're the things that are controversial. They are the things there is political controversy about. Public servants sometimes complain that senators pass over programs costing millions and look at programs costing mere thousands, but that is because the thousands are controversial and difficult, and the programs costing millions are well understood and don't involve controversy and difficulty. There is a focus on the matters that cause difficulty and controversy, certainly.
The capacity is there for senators to go fairly deeply into programs they're interested in.