How do you raise the total level cap of the Guiding Lands?

Every region in the endgame area of Iceborne, the Guiding Lands, has its own level, which can be increased or lowered by hunting specific monsters. At higher levels, stronger monsters appear, but the total level of all regions is capped, making it only possible to bring three areas to level 7, one to level 5, and two to level 1.

Is it known, however, that hunting large numbers of monsters in the Guiding Lands can slowly increase the total level cap, making it possible - in theory - to raise every area to level 7. Beyond this fact, there is much confusion and conflicting information about what exactly is needed to raise the level cap, so I am looking for answers to three strictly related questions, preferably with reliable sources.

1. Some people claim only tier 3 tempered monsters count towards raising the level cap. Can any large monster raise the level cap? If not, which monsters count? In either case, are some monsters worth more than others?
2. Does your Guiding Lands need to be unlocked in order to increase the level cap, or can I lock the levels so as to not lose the chance of spawning tier 3 tempered monsters?
3. Does hunting large monsters in other hunters' Guiding Lands count towards raising the cap of your own Guiding Lands? It is possible to affect your own region levels by joining someone else's Guiding Lands, so it would make sense for the level cap to be affected in a similar way.