Though i really like these ideas, i have to correct you on this one. You see, all non-public areas will have the same level enemies as the mission you started. This is an old trick for completing the Pocket Infinity Bounty, you need to make kills during nightfall, if soloing it with a fusion is too hard for you, you can just start it, and go to an opposite direction and find an easier non-public area to make your kills. They will be the same level and the modifiers like burns will be active.

I'm doing that bounty currently and my stupid ass never thought to try that. Dude I swear if it still works Im might cry, thank you so much lmao

With this being said what about the areas where there are level 30 vex just on Venus (not sure if it's classed as a "public area") but there's the place where two axis Minotaurs are and behind them the narrow staircase to where beyond it level 30 vex are.

It's also the same with the dead ghost in the gate lord area (on top of all the rocks) even once you've gotten it when you load up the vault of glass you can get it again although this time it has a more golden tint to it. Depending on the grimoire behind it, it could be another hint.