Mainly in the d e and f range. Even boosted to 10 you do not get enough keys every run to keep the cycle going. Once you get around 60 or so this is the only challenging solo stuff, so I like to play it a lot. Only it takes way to long to grind up to start runs, then to have to stop playing them just to get more keys kills the mood. IMHO it should be based on my skill if I can keep going, not on a rng drop rate.
Thank you for this wonderful game, I really enjoy playing it. Alas, the key thing is killing me. Work is supper slammed and so now the only time I have to play is spent farming keys and not having fun. Thanks for listening.