I had reached a plataeu of dose effectiveness - which was pretty good. Wanting to get on with doses lately I would skip using Condition. That worked fine for a few days, but then the doses started to lose some of the details that I like. I put condition back into my routine and that has helped a lot. I also started getting even deeper into the zone by using a couple of new techniques.
I have realized that listening to doses is a lot like daydreaming. You mind has to be in that creative wandering mode - only it is the dose that directs things rather than your imagination. You have to disengage your own mind as if entering a daydream.
One test I've found for how deep I am is ask what do I see? If I see the black behind my eyelids and nothing else, my mind is too active. You have to let the 18hz buzz move to the back of your head and let go of your vision centers. You will start to see random faint spashes of color - just let them come. Once that starts I quickly drift much deeper into the dose.