Where does the Character Movement Component.cpp discover a floor when falling?

I’m having trouble finding where a floor is discovered when falling in the Character Movement Component.cpp. I’m trying to modify the rules for what constitutes a valid floor. When the character walks off a surface they enter the Physfalling method. This falling does a lot of checks and stuff so I’m a little lost on where it’s actually discovering the floor below. Does it just wait until a collision occurs? What if I’m not using collision and I want to implement something that is more height based, like anything below X is a floor. I want to modify the CMC to acknowledge this and act accordingly.