It's hard to measure as those stats are for those who are newly coming and most undocumented immigrants have been here more than 10+ years, also many go under the radar.

That said I did make a mistake, I had read somewhere it was above 90% but on searching again it was referring to "non-central america undocumenteds" not all as a whole. But that doesn't change that hardly anyone comes wandering through a desert and climbing over a wall/fence.