That is one of the questions I had, It seems like the people who ride them with 4” of travel depend on them as part of their “standard suspension” . The fact is they are meant to be “bump stops” separate from your main suspension.
I have talked with a couple people that say buy the 4” one and you can limit the travel in them with spacer rings. Others say get the 2” because it is annoying hearing them constantly clanking against the axle.