There are a few common factors in his stories that also relate to other stories that utilize multidimensional/time travel stories. I will try and list the major ones for first:
John and Argent.
Main character John at the start is dying of Cancer.
Definitely a man with nothing to lose since that is a hard way to die.
Someone with nothing to lose can and will push the limits on what they can get from the aliens. He does that from the very beginning to some extents.
The aliens are also using him to add new genes to the people of that dimension. A male can spread the genetic materials faster than a female will. There are technical terms for that kind of a breeding program but why bother with those terms. Of course the main character is not told that is the reason for having so many mates.
Other writers and stories have used some of the same points with their Main Characters. It explains why at times they can and will push the limits way past what was originally offered and in many cases get what they ask for.