hOW WOULD YOU MAKE DIVE TABLES FOR THE VARIOUS COMBINATIONS???
I would suggest that the very reason we are discussing this is that it is too complicated to effectively learn in basic dive classes.
This is true, but there is even more to it than that.
As people have known for many decades, perhaps a century, individual divers and their personal physiologies vary in their risk of DCS. The most recent studies emphasize that. Ideally, we would have different tables for different people, but that is an obvious impossibility. So what happened is that testing for dive tables over the decades involved a lot of different people with a lot of different physiologies. If 23% (or whatever) of the population has a PFO, then the odds are that 23% of the people engaged in those tests had PFOs. When everything was done, they created dive tables that were deemed to be relatively safe for that wide variety of people. Some are safer than others, but pretty much everyone who dives should feel included in that spectrum of safety.
With the exception of some work by Buhlmann and maybe some others I don't know about, these tests were done at sea level. They were done under a variety of climatic conditions--air pressure, humidity, density, temperature, etc. None of those were at extremes, of course, but they covered the kind of weather conditions divers would likely encounter. It would be nice to have separate tables for separate weather conditions, but that is not possible. When the tables were done, they included conditions that were deemed to be relatively safe for the variety of weather conditions divers would encounter.
If you truly understand why diving at altitude needs to have adjustments, you will know that the reasons to be concerned vary with the altitude, the depth, and the length of the dive. If you are doing a relatively shallow recreational dive at 2,000 feet elevation, you really don't have to do a lot different from what you would do at sea level. Do the same dive at 6,000 feet, and you should be making adjustments. Do a deco dive at 6,000 feet, and you need to be very aware of the difference. If you are diving above 10,000 feet elevation, remember that the US Navy manual says that you should not so such a dive without special clearance, and that warning is in bright red, bold-faced letters.