For you guys wanting to make your crouch low crouch and the low crouch prone, Here's how you do it. FOR SHADOW OF CHERNOBYL ONLY!
Open your actor.ltx file and look for these lines
ph_box0_center = 0.0, 0.9, 0.0
ph_box0_size = 0.35, 0.9, 0.35
ph_box1_center = 0.0, 0.75, 0.0
ph_box1_size = 0.35, 0.75, 0.35
ph_box2_center = 0.0, 0.6, 0.0
ph_box2_size = 0.35, 0.6, 0.35
Change them to this.
ph_box0_center = 0.0, 0.9, 0.0
ph_box0_size = 0.35, 0.9, 0.35
ph_box1_center = 0.0, 0.65, 0.0
ph_box1_size = 0.35, 0.65, 0.35
ph_box2_center = 0.0, 0.2, 0.0
ph_box2_size = 0.35, 0.2, 0.35
You can now go prone and crawl under things! Just be careful where you stand up because you might get stuck and be unable to move.