I believe this is on a 98 mm last and a medium fit throughout. Works well for me. The plastics are quite thick and can be ground or punched to provide extra room. The performance liner is relatively thin and has a neoprene toe box. This liner does not seem very prone to packing out.
I agree that the HR has a medium volume fit throughout. The heel is not narrow, though... Not even relatively narrow. It is medium and it does not fit narrower heels well (IMO). The boot is relatively high over the instep!