When nage is attacked Yokomen, and he steps back tenshin, he then atemis to uke's face with his free arm, moving his center forward. The point is, you don't want to step back receiving yokomen and then collapse. You want to feel like your energy is moving fwd, even though you stepped back tenshin.
Ryotetori hajiki goshi - nage in right hanmi: irimi to uke's left side and move your right hand up to uke's left elbow, with your palm up (your thumb is up or toward the outside). Your left hand grabs uke's right forearm. Tenkan on your right foot and make uke take a step. When uke takes a step, then you throw him in hajiki goshi.
When you start a technique you are in hanmi. When you finish your throw, you are in toistai. You have to be aware of how you place your feet when doing tenshin or tenkan, so that you end up in toistai and not regular hanmi.