I see what you're saying. VT said that he had one arm on Joanna's back to kiss her but when she screamed, he put his other hand across her mouth. He said that when he took his hand off her mouth she screamed again, he put his hand back on her mouth and moved his other arm from her back to her throat. Per his story, 20 seconds later she went limp and presumably fell to the ground. As soon as he had one hand on her mouth and the other on her throat, unless she was backed against a solid surface, she would have run away. Furthermore, who puts one hand across a woman's mouth and another on her throat because she doesn't want to be kissed? She would have stopped screaming as soon as he left the flat ... there was no reason to prevent her from breathing.
I suspect that the attack started in the front hall right at the door. I seem to recall that there may be one or two steps down when entering the flat. I think that Joanna went backward, knocking over the coat rack and she was pinned either against the wall between the bathroom and bedroom doors, or she was pinned on the floor. I really doubt that this happened in the kitchen, where VT claims it happened. I don't see Joanna allowing herself to be cornered in the kitchen with a complete stranger. Even if he was an invited guest, he would not be in the kitchen.
Here is the floor plan, and below a view into the kitchen window. We see that there is a door between the kitchen and the dining area (thanks to the person that posted this earlier ... sorry, don't remember who that was).