when US Cartool designed them they were for improving chassis flex on the unibody, not for backing up coil overs. But structurally they box the frame, firewall, cowl, and upper shock mount. They also form a decent sized structural member if you consider the inner fender as the opposite side. Not all that different than the US Cartool subframes using the floor pan and the top of the box. It basically makes a frame stub that ties in the top of the shock mount, adding additional resistance to vertical flex between the cantilever frame rail and the cowl, which normally is just supported by the inner fender. They capture that whole corner between the firewall, cowl and inner fender, so they're pretty strong
