Some recent changes have happened.
Im fairly certain you are talking about the old habit, where the game would tell you that "X critter is almost up the stairs’ and etc. Yea. Ive been playing with the option for zlevels on for a quite a while now, and Ive noticed especially lately with my testing of my own custom made maps that critters can go up and down stairs if their query is traceable up there. Or im nuts and imagining it. thats happened a few times.
But no, I know that a recent pull request was talking about critters being able to see and fire at different levels, and I think it did say something about basic pathing around levels in cases where the impetus is present strongly enough.