Genetic? As in, some breeds are more prone to RG than others? Is that what you mean? "Reptile" kind of hits me wrong, lol.... ? Reptile when talking about a dog? What am I missing here ?
IMHO, I will say denial of the bed is the way to go here.
"Reptile brain" is a common term among biologists to indicate the inner parts of the brain that are concerned primarily with survival. It operates at the subconscious level. This is as opposed to the next layer out, the mammalian part and the "frontal lobes" that have more reasoning skills.
All of us have all these layers. Your "reptile brain" is what gets triggered when approached by a mugger. It helps you react appropriately: fight or flight, to survive. RG is very much something that happens at this level of consciousness.... that is without much "reasoning" involved. Incidentally, the "reptile brain" is also where most of your emotional life is located.
If you've seen a dog in full RG mode, he appears to think his very survival is at stake over his toy or food bowl. Of course long ago, that was the case, as a bit of bone or a food source could indeed be the difference between life and death.
That explained, I have no trouble with restricting access to the bed, as I stated with Furbaby. So long as that can be accomplished without activating the RG issue in the first place, that is easy. For example closing the door. (If you read Crio's sticky, you will see this is recommended.)
In the long run, I find it is much nicer to "re-train the reptile brain" not to feel threatened in these situations. So for example, my boy Josey, who used to get quite agitated if I approached him while eating, now welcomes me as I've reconditioned his brain to know that only good things happen when I approach at meal times.
The OP can easily create the same sort of pleasant associations with the pom with regard to her approach to the dog whilst he is on the bed. It just takes consistent repetition of pairing the stimulus with something pleasant, to change the emotional response.