Trace hit even if inside an bigger object

Hello, how can I make my trace generate hits even if whole trace line is inside an bigger object.
I am doing ledge grabbing and everything is good but I want my character not to be able to grab if there is not enough space (like 10 cm at least) above the ledge. I am doing the line trace but if it is whole inside in object (line do not cross any of collision faces) it do not generate any hits.