Ask those of us that do the catching and you'll get varied estimates based on what they have seen in person.
I generally use 33% ratio and yes it's an estimate, because that's all you can do.
Some days we catch 10% and some days we catch 90%, but on the average I'd bet my career we don't catch more then a third, on the average. We just don't have the man power.
Have 3 million gotten by us this year? It’s entirely possible. I’d bet it’s lower, probably more like 2 million or just under.
And it's the folks not on the ground that make the official reports the government uses to determine funding, and the press releases that make the headlines. I'm sure the guys on the ground have an excellent understanding of how effective they're being, but privates don't write press releases. Officially, according to the reports, you only catch 10%, whether you catch 2 or 2 million doesn't matter, the official estimate are that the number of guys you catch is 10% of total attempted illegal crossings.