I don't know why it imposes it on the man. The woman should be paying attention to the man even in missionary. The man may want to stop.
You don't have to be looking constantly at your sexual partner but you need to be looking often enough to notice any changes. I mean I have mentioned in at least one previous post that healthy sex and consent is about good communication between both partners. People so often want to separate the the verbal and the non verbal but they come as a package. In the ideal world, everyone would be able to say when they aren't comfortable. In the absence of that, there are multiple other cues available.
I think it's important to remember that survival responses kick in because of traumatic experiences. I also think a part of maybe both our frustration is that beyond what we are trying to pin down here to create almost a definitive guide, is actually there is an element of instinct involved.
For example, because of my personal experiences with abuse, in one of the first times I had sex with my partner I misread a facial expression he had. I thought he was in pain and wanted to stop, actually his expression was from arousal build up (that point where it feels slightly overwhelming). Anyway the point was that I stopped and asked.
Really that's all we can reaps ably expect.
As I'm writing I'm thinking about the every day man or woman who has no intent to harm or put themselves before others. I may still have an element of naivety maybe but I like to believe that if we don't want to hurt someone that way (and were not an abuser convincing themselves people want us really), then we naturally wouldn't behave in an abusive way.