Maybe you haven’t gotten terribly far in end game this league yet in Path of Exile, so do you want to know how to make bosses more worthwhile and Atlas completion more attractive? Of course, having enough poe orbs is a prerequisite. Perhaps the following advice is not the best, but it will certainly help you.
In Path of Exile, all bosses have a guaranteed map drop. The guaranteed drop is equal to ‘Current Tier-1’ for white maps, -2 for yellow maps, and -3 for red maps. This means completing a T5 guarantees you at least a T4 map from the boss (can roll better). Atlas completion bonus applies to this drop. So getting at least 100/157 means the drop is equal tier for white, -1 for yellow, and -2 for red maps.
Then, you should adding more bonuses for Atlas completion: Every map completed after 100/157 adds a 1% chance for the boss to drop an additional map. Maps dropped from this ‘bonus roll’ would have the ‘minimum tier level’ bonus for bosses applied to them.
Having 157/157 completion increases the level of maps dropped specifically by the boss (guaranteed AND normal/bonus drops) by an additional +1. This means the guaranteed map drops from the boss will be at minimum +1 tier for white maps (not beneficial at that stage, but whatever), equal tier for yellow, and -1 for red maps. They can still roll higher, as normal.
Personally some players don’t think map sustain should be as difficult as it is currently and they are fine with something like this, they do think this system should only apply though if you meet bonus map requirements, etc must be magic for white, rare for yellow, and corrupted for red.