PhysX collisions on infantry units (such as the one used in the BIN_fnc_setRagdoll function from the Contact DLC) only work within a 100 meters radius from the current camera. Beyond that range, physX objects used as colliders seem to go through units without any effect.
Tested on :
Game version: 2.06.148470
Branch: main
Use the BIN_fnc_setRagdoll function on any unit that is located further than 100 meters from the player (or the current camera). See the Repro Mission : use the action menu to call BIN_fnc_setRagdoll or the custom function (fn_collid) included in the scenario.
Although this is a minor issue for vanilla Arma3, the BIN_fnc_setRagdoll function from Contact is severly limited by this. Increasing the 100 meters range (or getting rid of it) would also open up a lot of possibilities for mod & mission makers.
Another observation : EPEContact event handlers are properly triggered, even beyond 100 meters, and as far as I know, there's no range limit on the simulation of physX objects; so the issue likely comes from some sort of limitation on infantry units themselves.