...Just realized this could also mean no room for our arm at all: I would guess to use the torso to walk into the place where the tegatana would be.
Yup. I've been on the receiving end of some quite effective ikkyos where the contact with my elbow was my partner's torso or upper thigh. There are also some fun variations involving a knee to the chest or a kick in the face with the inside leg. The ikkyo-to-koshinage variations have lots of atemi with the free ("elbow") hand to help make space to get the hips in.
All of which are sort of pointless to discuss without video or hands-on demonstrations, but so it goes.