Waystones: How many portals are you supposed to get?

For end-game maps (waystones). I always get 6 on a white or blue map. And 1 on a yellow (rare) map with 6 affixes. But for some reason, the amount I get on a rare, 4 affix map varies. I've gotten 2, 3, 4, or 5 portals. Usually 3. Is this a bug or intended? I'm not using anything that gives me extra or fewer revives (like the Doryani passive). If intended, it makes zero sense to me. Kinda makes using the Doryani passive useless on a 4 affix rare map cause u might end up with 5 portals without him, and not need him. And the unpredictabilty of it is just bad in general. What has your guys' experience been, and do we have word from GGG on how this is supposed to actually work? Thanks!